This section describes the configuration file in detail.

There is one point that should be made clear immediately: the syntax of the configuration file is designed to be reasonably easy to parse, since this is done every time sendmail starts up, rather than easy for a human to read or write. On the future project list is a configuration-file compiler.

The configuration file is organized as a series of lines, each of which begins with a single character defining the semantics for the rest of the line. Lines beginning with a space or a tab are continuation lines (although the semantics are not well defined in many places). Blank lines and lines beginning with a sharp symbol (`#') are comments.

R and S -- Rewriting Rules

The core of address parsing are the rewriting rules. These are an ordered production system. Sendmail scans through the set of rewriting rules looking for a match on the left hand side (LHS) of the rule. When a rule matches, the address is replaced by the right hand side (RHS) of the rule.

There are several sets of rewriting rules. Some of the rewriting sets are used internally and must have specific semantics. Other rewriting sets do not have specifically assigned semantics, and may be referenced by the mailer definitions or by other rewriting sets.

The syntax of these two commands are:

S n
Sets the current ruleset being collected to n. If you begin a ruleset more than once it appends to the old definition.
R lhs rhs comments
The fields must be separated by at least one tab character; there may be embedded spaces in the fields. The lhs is a pattern that is applied to the input. If it matches, the input is rewritten to the rhs. The comments are ignored.

Macro expansions of the form $ x are performed when the configuration file is read. Expansions of the form $& x are performed at run time using a somewhat less general algorithm. This for is intended only for referencing internally defined macros such as $h that are changed at runtime.

The left hand side

The left hand side of rewriting rules contains a pattern. Normal words are simply matched directly. Metasyntax is introduced using a dollar sign. The metasymbols are:

$* Match zero or more tokens
$+ Match one or more tokens
$- Match exactly one token
$=x Match any phrase in class x
$~x Match any word not in class x
If any of these match, they are assigned to the symbol $ n for replacement on the right hand side, where n is the index in the LHS. For example, if the LHS:
is applied to the input:
the rule will match, and the values passed to the RHS will be:

$2 eric

Additionally, the LHS can include $@ to match zero tokens. This is not bound to a $ n on the RHS, and is normally only used when it stands alone in order to match the null input.

The right hand side

When the left hand side of a rewriting rule matches, the input is deleted and replaced by the right hand side. Tokens are copied directly from the RHS unless they begin with a dollar sign. Metasymbols are:

$n Substitute indefinite token n from LHS
$[name$] Canonicalize name
$(map key $@arguments $:default $)
Generalized keyed mapping function
$>n "Call" ruleset n
$#mailer Resolve to mailer
$@host Specify host
$:user Specify user

The $ n syntax substitutes the corresponding value from a $+, $-, $*, $=, or $~ match on the LHS. It may be used anywhere.

A host name enclosed between $[ and $] is looked up in the host database(s) and replaced by the canonical name[14]. For example, $[ftp$] might become ftp.CS.Berkeley.EDU and $[[]$] would become vangogh.CS.Berkeley.EDU. Sendmail recognizes it's numeric IP address without calling the name server and replaces it with it's canonical name.

The $( ... $) syntax is a more general form of lookup; it uses a named map instead of an implicit map. If no lookup is found, the indicated default is inserted; if no default is specified and no lookup matches, the value is left unchanged. The arguments are passed to the map for possible use.

The $> n syntax causes the remainder of the line to be substituted as usual and then passed as the argument to ruleset n. The final value of ruleset n then becomes the substitution for this rule. The $> syntax can only be used at the beginning of the right hand side; it can be only be preceded by $@ or $:.

The $# syntax should only be used in ruleset zero or a subroutine of ruleset zero. It causes evaluation of the ruleset to terminate immediately, and signals to sendmail that the address has completely resolved. The complete syntax is:

$#mailer $@host $:user
This specifies the {mailer, host, user} 3-tuple necessary to direct the mailer. If the mailer is local the host part may be omitted[15]. The mailer must be a single word, but the host and user may be multi-part. If the mailer is the builtin IPC mailer, the host may be a colon-separated list of hosts that are searched in order for the first working address (exactly like MX records). The user is later rewritten by the mailer-specific envelope rewriting set and assigned to the $u macro. As a special case, if the mailer specified has the F=@ flag specified and the first character of the $: value is @, the @ is stripped off, and a flag is set in the address descriptor that causes sendmail to not do ruleset 5 processing.

Normally, a rule that matches is retried, that is, the rule loops until it fails. A RHS may also be preceded by a $@ or a $: to change this behavior. A $@ prefix causes the ruleset to return with the remainder of the RHS as the value. A $: prefix causes the rule to terminate immediately, but the ruleset to continue; this can be used to avoid continued application of a rule. The prefix is stripped before continuing.

The $@ and $: prefixes may precede a $> spec; for example:

R$+ $: $>7 $1
matches anything, passes that to ruleset seven, and continues; the $: is necessary to avoid an infinite loop.

Substitution occurs in the order described, that is, parameters from the LHS are substituted, hostnames are canonicalized, subroutines are called, and finally $#, $@, and $: are processed.

Semantics of rewriting rule sets

There are five rewriting sets that have specific semantics. Four of these are related as depicted by figure 1.

                 -->| 0 |-->resolved address
                /   +---+
               /            +---+   +---+
              /        ---->| 1 |-->| S |--
       +---+ / +---+  /     +---+   +---+  \    +---+
addr-->| 3 |-->| D |--                      --->| 4 |-->msg
       +---+   +---+  \     +---+   +---+  /    +---+
                        --->| 2 |-->| R |--
                            +---+   +---+

see ASCII picture above

Figure 1 -- Rewriting set semantics

D -- sender domain addition
S -- mailer-specific sender rewriting
R -- mailer-specific recipient rewriting

Ruleset three should turn the address into canonical form. This form should have the basic syntax:

Ruleset three is applied by sendmail before doing anything with any address.

If no @ sign is specified, then the host-domain-spec may be appended (box D in Figure 1) from the sender address (if the C flag is set in the mailer definition corresponding to the sending mailer).

Ruleset zero is applied after ruleset three to addresses that are going to actually specify recipients. It must resolve to a {mailer, host, user} triple. The mailer must be defined in the mailer definitions from the configuration file. The host is defined into the $h macro for use in the argv expansion of the specified mailer.

Rulesets one and two are applied to all sender and recipient addresses respectively. They are applied before any specification in the mailer definition. They must never resolve.

Ruleset four is applied to all addresses in the message. It is typically used to translate internal to external form.

In addition, ruleset 5 is applied to all local addresses (specifically, those that resolve to a mailer with the `F=5' flag set) that do not have aliases. This allows a last minute hook for local names.

Ruleset hooks

A few extra rulesets are defined as hooks that can be defined to get special features. They are all named rulesets. The check_* forms all give accept/reject status; falling off the end or returning normally is an accept, and resolving to $#error is a reject.


The check_relay ruleset is called after a connection is accepted. It is passed $|
where $| is a metacharacter separating the two parts. This ruleset can reject connections from various locations.


The check_mail ruleset is passed the user name parameter of the SMTP MAIL command. It can accept or reject the address.


The check_rcpt ruleset is passed the user name parameter of the SMTP RCPT command. It can accept or reject the address.


The check_compat ruleset is passed

sender-address $| recipient-address
where $| is a metacharacter separating the addresses. It can accept or reject mail transfer between these two addresses much like the checkcompat() function.

IPC mailers

Some special processing occurs if the ruleset zero resolves to an IPC mailer (that is, a mailer that has [IPC] listed as the Path in the M configuration line. The host name passed after $@ has MX expansion performed; this looks the name up in DNS to find alternate delivery sites.

The host name can also be provided as a dotted quad in square brackets; for example:

This causes direct conversion of the numeric value to a TCP/IP host address.

The host name passed in after the $@ may also be a colon-separated list of hosts. Each is separately MX expanded and the results are concatenated to make (essentially) one long MX list. The intent here is to create fake MX records that are not published in DNS for private internal networks.

As a final special case, the host name can be passed in as a text string in square brackets:

This form avoids the MX mapping. N.B.: This is intended only for situations where you have a network firewall or other host that will do special processing for all your mail, so that your MX record points to a gateway machine; this machine could then do direct delivery to machines within your local domain. Use of this feature directly violates RFC 1123 section 5.3.5: it should not be used lightly.

D -- Define Macro

Macros are named with a single character or with a word in {braces}. Single character names may be selected from the entire ASCII set, but user-defined macros should be selected from the set of upper case letters only. Lower case letters and special symbols are used internally. Long names beginning with a lower case letter or a punctuation character are reserved for use by sendmail, so user-defined long macro names should begin with an upper case letter.

The syntax for macro definitions is:

D xval
where x is the name of the macro (which may be a single character or a word in braces) and val is the value it should have. There should be no spaces given that do not actually belong in the macro value.

Macros are interpolated using the construct $ x, where x is the name of the macro to be interpolated. This interpolation is done when the configuration file is read, except in M lines. The special construct $& x can be used in R lines to get deferred interpolation.

Conditionals can be specified using the syntax:

$?x text1 $| text2 $.
This interpolates text1 if the macro $x is set, and text2 otherwise. The else ( $|) clause may be omitted.

Lower case macro names are reserved to have special semantics, used to pass information in or out of sendmail, and special characters are reserved to provide conditionals, etc. Upper case names (that is, $A through $Z) are specifically reserved for configuration file authors.

The following macros are defined and/or used internally by sendmail for interpolation into argv's for mailers or for other contexts. The ones marked * are information passed into sendmail[16], the ones marked are information passed both in and out of sendmail, and the unmarked macros are passed out of sendmail but are not otherwise used internally. These macros are:

The origination date in RFC 822 format. This is extracted from the Date: line.
The current date in RFC 822 format.
The hop count. This is a count of the number of Received: lines plus the value of the -h command line flag.
The current date in UNIX (ctime) format.
(Obsolete; use SmtpGreetingMessage option instead.) The SMTP entry message. This is printed out when SMTP starts up. The first word must be the $j macro as specified by RFC821. Defaults to $j Sendmail $v ready at $b. Commonly redefined to include the configuration version number, e.g., $j Sendmail $v/$Z ready at $b
The envelope sender (from) address.
The sender address relative to the recipient. For example, if $f is foo, $g will be host!foo, foo@host.domain, or whatever is appropriate for the receiving mailer.
The recipient host. This is set in ruleset 0 from the $# field of a parsed address.
The queue id, e.g., HAA12345.
The "official" domain name for this site. This is fully qualified if the full qualification can be found. It must be redefined to be the fully qualified domain name if your system is not configured so that information can find it automatically.
The UUCP node name (from the uname system call).
(Obsolete; use UnixFromLine option instead.) The format of the UNIX from line. Unless you have changed the UNIX mailbox format, you should not change the default, which is From $g $d.
The domain part of the gethostname return value. Under normal circumstances, $j is equivalent to $w.$m.
The name of the daemon (for error messages). Defaults to MAILER-DAEMON.
(Obsolete: use OperatorChars option instead.) The set of "operators" in addresses. A list of characters which will be considered tokens and which will separate tokens when doing parsing. For example, if @ were in the $o macro, then the input a@b would be scanned as three tokens: a, @, and b. Defaults to .:@[], which is the minimum set necessary to do RFC 822 parsing; a richer set of operators is .:%@!/[], which adds support for UUCP, the %-hack, and X.400 addresses.
Sendmail's process id.
Default format of sender address. The $q macro specifies how an address should appear in a message when it is defaulted. Defaults to <$g>. It is commonly redefined to be $?x$x <$g>$|$g$. or $g$?x ($x)$., corresponding to the following two formats:
Eric Allman <eric@CS.Berkeley.EDU>
eric@CS.Berkeley.EDU (Eric Allman)
Sendmail properly quotes names that have special characters if the first form is used.
Protocol used to receive the message. Set from the -p command line flag or by the SMTP server code.
Sender's host name. Set from the -p command line flag or by the SMTP server code.
A numeric representation of the current time.
The recipient user.
The version number of the sendmail binary.
The hostname of this site. This is the root name of this host (but see below for caveats).
The full name of the sender.
The home directory of the recipient.
The validated sender address.
The message body type (7BIT or 8BITMIME), as determined from the envelope.
The IP address of the SMTP client. Defined in the SMTP server only.
The host name of the SMTP client. Defined in the SMTP server only.
The port number of the SMTP client. Defined in the SMTP server only.
The envelope id passed to sendmail as part of the envelope.
The current operation mode (from the -b flag).

There are three types of dates that can be used. The $a and $b macros are in RFC 822 format; $a is the time as extracted from the Date: line of the message (if there was one), and $b is the current date and time (used for postmarks). If no Date: line is found in the incoming message, $a is set to the current time also. The $d macro is equivalent to the $b macro in UNIX (ctime) format.

The macros $w, $j, and $m are set to the identity of this host. Sendmail tries to find the fully qualified name of the host if at all possible; it does this by calling gethostname(2) to get the current hostname and then passing that to gethostbyname(3) which is supposed to return the canonical version of that host name.[17] Assuming this is successful, $j is set to the fully qualified name and $m is set to the domain part of the name (everything after the first dot). The $w macro is set to the first word (everything before the first dot) if you have a level 5 or higher configuration file; otherwise, it is set to the same value as $j. If the canonification is not successful, it is imperative that the config file set $j to the fully qualified domain name[18].

The $f macro is the id of the sender as originally determined; when mailing to a specific host the $g macro is set to the address of the sender relative to the recipient. For example, if I send to bollard@matisse.CS.Berkeley.EDU from the machine vangogh.CS.Berkeley.EDU the $f macro will be eric and the $g macro will be eric@vangogh.CS.Berkeley.EDU.

The $x macro is set to the full name of the sender. This can be determined in several ways. It can be passed as flag to sendmail. It can be defined in the NAME environment variable. The third choice is the value of the Full-Name: line in the header if it exists, and the fourth choice is the comment field of a From: line. If all of these fail, and if the message is being originated locally, the full name is looked up in the /etc/passwd file.

When sending, the $h, $u, and $z macros get set to the host, user, and home directory (if local) of the recipient. The first two are set from the $@ and $: part of the rewriting rules, respectively.

The $p and $t macros are used to create unique strings (e.g., for the Message-Id: field). The $i macro is set to the queue id on this host; if put into the timestamp line it can be extremely useful for tracking messages. The $v macro is set to be the version number of sendmail; this is normally put in timestamps and has been proven extremely useful for debugging.

The $c field is set to the hop count, i.e., the number of times this message has been processed. This can be determined by the -h flag on the command line or by counting the timestamps in the message.

The $r and $s fields are set to the protocol used to communicate with sendmail and the sending hostname. They can be set together using the -p command line flag or separately using the -M or -oM flags.

The $_ is set to a validated sender host name. If the sender is running an RFC 1413 compliant IDENT server and the receiver has the IDENT protocol turned on, it will include the user name on that host.

The ${client_name}, ${client_addr}, and ${client_port} macros are set to the name, address, and port number of the SMTP client who is invoking sendmail as a server. These can be used in the check_* rulesets (using the $& deferred evaluation form, of course!).

C and F -- Define Classes

Classes of phrases may be defined to match on the left hand side of rewriting rules, where a phrase is a sequence of characters that do not contain space characters. For example a class of all local names for this site might be created so that attempts to send to oneself can be eliminated. These can either be defined directly in the configuration file or read in from another file. Classes are named as a single letter or a word in {braces}. Class names beginning with lower case letters and special characters are reserved for system use. Classes defined in config files may be given names from the set of upper case letters for short names or beginning with an upper case letter for long names.

The syntax is:

C cphrase1 phrase2...
F cfile
The first form defines the class c to match any of the named words. It is permissible to split them among multiple lines; for example, the two forms:
CHmonet ucbmonet
are equivalent. The ``F'' form reads the elements of the class c from the named file.

Elements of classes can be accessed in rules using $= or $~. The $~ (match entries not in class) only matches a single word; multi-word entries in the class are ignored in this context.

Some classes have internal meaning to sendmail:

contains the Content-Transfer-Encodings that can be 8->7 bit encoded. It is predefined to contain 7bit, 8bit, and binary.
set to be the same as $k, that is, the UUCP node name.
set to the set of domains by which this host is known, initially just $m.
can be set to the set of MIME body types that can never be eight to seven bit encoded. It defaults to multipart/signed. Message types message/* and multipart/* are never encoded directly. Multipart messages are always handled recursively. The handling of message/* messages are controlled by class $=s.
A set of Content-Types that will never be encoded as base64 (if they have to be encoded, they will be encoded as quoted-printable). It can have primary types (e.g., text) or full types (such as text/plain). The class is initialized to have text/plain only.
contains the set of subtypes of message that can be treated recursively. By default it contains only rfc822. Other message/* types cannot be 8->7 bit encoded. If a message containing eight bit data is sent to a seven bit host, and that message cannot be encoded into seven bits, it will be stripped to 7 bits.
set to the set of trusted users by the T configuration line. If you want to read trusted users from a file use Ft /file/name.
set to be the set of all names this host is known by. This can be used to match local hostnames.

Sendmail can be compiled to allow a scanf(3) string on the F line. This lets you do simplistic parsing of text files. For example, to read all the user names in your system /etc/passwd file into a class, use

FL/etc/passwd %[^:]
which reads every line up to the first colon.

M -- Define Mailer

Programs and interfaces to mailers are defined in this line. The format is:

M name, { field= value}*
where name is the name of the mailer (used internally only) and the field=name pairs define attributes of the mailer. Fields are:

Path The pathname of the mailer
Flags Special flags for this mailer
Sender Rewriting set(s) for sender addresses
Recipient Rewriting set(s) for recipient addresses
Argv An argument vector to pass to this mailer
Eol The end-of-line string for this mailer
Maxsize The maximum message length to this mailer
Linelimit The maximum line length in the message body
Directory The working directory for the mailer
Userid The default user and group id to run as
Nice The nice(2) increment for the mailer
Charset The default character set for 8-bit characters
Type The MTS type information (used for error messages)
Only the first character of the field name is checked.

The following flags may be set in the mailer description. Any other flags may be used freely to conditionally assign headers to messages destined for particular mailers. Flags marked with * are not interpreted by the sendmail binary; these are the conventionally used to correlate to the flags portion of the H line. Flags marked with apply to the mailers for the sender address rather than the usual recipient mailers.

Run Extended SMTP (ESMTP) protocol (defined in RFCs 1651, 1652, and 1653). This flag defaults on if the SMTP greeting message includes the word ESMTP.
Look up the user part of the address in the alias database. Normally this is only set for local mailers.
Force a blank line on the end of a message. This is intended to work around some stupid versions of /bin/mail that require a blank line, but do not provide it themselves. It would not normally be used on network mail.
Do not include comments in addresses. This should only be used if you have to work around a remote mailer that gets confused by comments. This strips addresses of the form Phrase <address> or address (Comment) down to just address.
If mail is received from a mailer with this flag set, any addresses in the header that do not have an at sign ( @) after being rewritten by ruleset three will have the @domain clause from the sender envelope address tacked on. This allows mail with headers of the form:
From: usera@hosta
To: userb@hostb, userc
to be rewritten as:
From: usera@hosta
To: userb@hostb, userc@hosta
automatically. However, it doesn't really work reliably.
Do not include angle brackets around route-address syntax addresses. This is useful on mailers that are going to pass addresses to a shell that might interpret angle brackets as I/O redirection.
This mailer wants a Date: header line.
This mailer is expensive to connect to, so try to avoid connecting normally; any necessary connection will occur during a queue run.
Escape lines beginning with From in the message with a `>' sign.
The mailer wants a -f from flag, but only if this is a network forward operation (i.e., the mailer will give an error if the executing user does not have special permissions).
This mailer wants a From: header line.
Normally, sendmail sends internally generated email (e.g., error messages) using the null return address as required by RFC 1123. However, some mailers don't accept a null return address. If necessary, you can set the g flag to prevent sendmail from obeying the standards; error messages will be sent as from the MAILER-DAEMON (actually, the value of the $n macro).
Upper case should be preserved in host names for this mailer.
Do User Database rewriting on envelope sender address.
This mailer will be speaking SMTP to another sendmail -- as such it can use special protocol features. This option is not required (i.e., if this option is omitted the transmission will still operate successfully, although perhaps not as efficiently as possible).
Do User Database rewriting on recipients as well as senders.
Normally when sendmail connects to a host via SMTP, it checks to make sure that this isn't accidently the same host name as might happen if sendmail is misconfigured or if a long-haul network interface is set in loopback mode. This flag disables the loopback check. It should only be used under very unusual circumstances.
Currently unimplemented. Reserved for chunking.
This mailer is local (i.e., final delivery will be performed).
Limit the line lengths as specified in RFC821. This deprecated option should be replaced by the L= mail declaration. For historic reasons, the L flag also sets the 7 flag.
This mailer can send to multiple users on the same host in one transaction. When a $u macro occurs in the argv part of the mailer definition, that field will be repeated as necessary for all qualifying users.
This mailer wants a Message-Id: header line.
Do not insert a UNIX-style From line on the front of the message.
Always run as the owner of the recipient mailbox. Normally sendmail runs as the sender for locally generated mail or as daemon (actually, the user specified in the u option) when delivering network mail. The normal behaviour is required by most local mailers, which will not allow the envelope sender address to be set unless the mailer is running as daemon. This flag is ignored if the S flag is set.
Use the route-addr style reverse-path in the SMTP MAIL FROM: command rather than just the return address; although this is required in RFC821 section 3.1, many hosts do not process reverse-paths properly. Reverse-paths are officially discouraged by RFC 1123.
This mailer wants a Return-Path: line.
When an address that resolves to this mailer is verified (SMTP VRFY command), generate 250 responses instead of 252 responses. This will imply that the address is local.
Same as f, but sends a -r flag.
Open SMTP connections from a secure port. Secure ports aren't (secure, that is) except on UNIX machines, so it is unclear that this adds anything.
Strip quote characters (" and \e) off of the address before calling the mailer.
Don't reset the userid before calling the mailer. This would be used in a secure environment where sendmail ran as root. This could be used to avoid forged addresses. If the U= field is also specified, this flag causes the user id to always be set to that user and group (instead of leaving it as root).
Upper case should be preserved in user names for this mailer.
This mailer wants UUCP-style From lines with the ugly remote from <host> on the end.
The user must have a valid account on this machine, i.e., getpwnam must succeed. If not, the mail is bounced. This is required to get .forward capability.
This mailer wants a Full-Name: header line.
This mailer want to use the hidden dot algorithm as specified in RFC821; basically, any line beginning with a dot will have an extra dot prepended (to be stripped at the other end). This insures that lines in the message containing a dot will not terminate the message prematurely.
Don't look up MX records for hosts sent via SMTP.
Extend the list of characters converted to =XX notation when converting to Quoted-Printable to include those that don't map cleanly between ASCII and EBCDIC. Useful if you have IBM mainframes on site.
If no aliases are found for this address, pass the address through ruleset 5 for possible alternate resolution. This is intended to forward the mail to an alternate delivery spot.
Strip all output to seven bits. This is the default if the L flag is set. Note that clearing this option is not sufficient to get full eight bit data passed through sendmail. If the 7 option is set, this is essentially always set, since the eighth bit was stripped on input. Note that this option will only impact messages that didn't have 8->7 bit MIME conversions performed.
If set, it is acceptable to send eight bit data to this mailer; the usual attempt to do 8->7 bit MIME conversions will be bypassed.
If set, do limited 7->8 bit MIME conversions. These conversions are limited to text/plain data.
Check addresses to see if they begin :include:; if they do, convert them to the *include* mailer.
Check addresses to see if they begin with a `|'; if they do, convert them to the prog mailer.
Check addresses to see if they begin with a `/'; if they do, convert them to the *file* mailer.
Look up addresses in the user database.

Configuration files prior to level 6 assume the `A', `w', `5', `:', `|', `/', and `@' options on the mailer named local.

The mailer with the special name error can be used to generate a user error. The (optional) host field is an exit status to be returned, and the user field is a message to be printed. The exit status may be numeric or one of the values USAGE, NOUSER, NOHOST, UNAVAILABLE, SOFTWARE, TEMPFAIL, PROTOCOL, or CONFIG to return the corresponding EX_ exit code, or an enhanced error code as described in RFC 1893, Enhanced Mail System Status Codes. For example, the entry:

$#error $@ NOHOST $: Host unknown in this domain
on the RHS of a rule will cause the specified error to be generated and the Host unknown exit status to be returned if the LHS matches. This mailer is only functional in rulesets 0, 5, or one of the check_* rulesets.

The mailer named local must be defined in every configuration file. This is used to deliver local mail, and is treated specially in several ways. Additionally, three other mailers named prog, *file*, and *include* may be defined to tune the delivery of messages to programs, files, and :include: lists respectively. They default to:

Mprog, P=/bin/sh, F=lsD, A=sh -c $u
M*file*, P=/dev/null, F=lsDFMPEu, A=FILE
M*include*, P=/dev/null, F=su, A=INCLUDE

The Sender and Recipient rewriting sets may either be a simple ruleset id or may be two ids separated by a slash; if so, the first rewriting set is applied to envelope addresses and the second is applied to headers.

The Directory is actually a colon-separated path of directories to try. For example, the definition D=$z:/ first tries to execute in the recipient's home directory; if that is not available, it tries to execute in the root of the filesystem. This is intended to be used only on the prog mailer, since some shells (such as csh) refuse to execute if they cannot read the home directory. Since the queue directory is not normally readable by unprivileged users csh scripts as recipients can fail.

The Userid specifies the default user and group id to run as, overriding the DefaultUser option (q.v.). If the S mailer flag is also specified, this is the user and group to run as in all circumstances. This may be given as user:group to set both the user and group id; either may be an integer or a symbolic name to be looked up in the passwd and group files respectively. If only a symbolic user name is specified, the group id in the passwd file for that user is used as the group id.

The Charset field is used when converting a message to MIME; this is the character set used in the Content-Type: header. If this is not set, the DefaultCharset option is used, and if that is not set, the value unknown-8bit is used. WARNING: this field applies to the sender's mailer, not the recipient's mailer. For example, if the envelope sender address lists an address on the local network and the recipient is on an external network, the character set will be set from the Charset= field for the local network mailer, not that of the external network mailer.

The Type= field sets the type information used in MIME error messages as defined by RFC 1894. It is actually three values separated by slashes: the MTA-type (that is, the description of how hosts are named), the address type (the description of e-mail addresses), and the diagnostic type (the description of error diagnostic codes). Each of these must be a registered value or begin with X-. The default is dns/rfc822/smtp.

H -- Define Header

The format of the header lines that sendmail inserts into the message are defined by the H line. The syntax of this line is:

H[ ? mflags ?] hname : htemplate
Continuation lines in this spec are reflected directly into the outgoing message. The htemplate is macro expanded before insertion into the message. If the mflags (surrounded by question marks) are specified, at least one of the specified flags must be stated in the mailer definition for this header to be automatically output. If one of these headers is in the input it is reflected to the output regardless of these flags.

Some headers have special semantics that will be described later.

O -- Set Option

There are a number of global options that can be set from a configuration file. Options are represented by full words; some are also representable as single characters for back compatibility. The syntax of this line is:

O option = value
This sets option option to be value. Note that there must be a space between the letter `O' and the name of the option. An older version is:
O ovalue
where the option o is a single character. Depending on the option, value may be a string, an integer, a boolean (with legal values t, T, f, or F; the default is TRUE), or a time interval.

The options supported (with the old, one character names in brackets) are:

AliasFile=spec, spec, ...
[A] Specify possible alias file(s). Each spec should be in the format `` class : file'' where class : is optional and defaults to ``implicit''. Depending on how sendmail is compiled, valid classes are implicit (search through a compiled-in list of alias file types, for back compatibility), hash (if NEWDB is specified), dbm (if NDBM is specified), stab (internal symbol table -- not normally used unless you have no other database lookup), or nis (if NIS is specified). If a list of specs are provided, sendmail searches them in order.
[a] If set, wait up to timeout (units default to minutes) for an @:@ entry to exist in the alias database before starting up. If it does not appear in the timeout interval rebuild the database (if the AutoRebuildAliases option is also set) or issue a warning.
[no short name] If set, allow HELO SMTP commands that don't include a host name. Setting this violates RFC 1123 section 5.2.5, but is necessary to interoperate with several SMTP clients. If there is a value, it is still checked for legitimacy.
[D] If set, rebuild the alias database if necessary and possible. If this option is not set, sendmail will never rebuild the alias database unless explicitly requested using -bi. Not recommended -- can cause thrashing.
[B] Set the blank substitution character to c. Unquoted spaces in addresses are replaced by this character. Defaults to space (i.e., no change is made).
[n] Validate the RHS of aliases when rebuilding the alias database.
[C] Checkpoints the queue every N (default 10) addresses sent. If your system crashes during delivery to a large list, this prevents retransmission to any but the last N recipients.
[z] The indicated factor is multiplied by the message class (determined by the Precedence: field in the user header and the P lines in the configuration file) and subtracted from the priority. Thus, messages with a higher Priority: will be favored. Defaults to 1800.
[no short name] If set, colons are acceptable in e-mail addresses (e.g., host:user). If not set, colons indicate the beginning of a RFC 822 group construct ( groupname: member1, member2, ... memberN;). Doubled colons are always acceptable ( nodename::user) and proper route-addr nesting is understood ( <@relay:user@host>). Furthermore, this option defaults on if the configuration version level is less than 6 (for back compatibility). However, it must be off for full compatibility with RFC 822.
[k] The maximum number of open connections that will be cached at a time. The default is one. This delays closing the current connection until either this invocation of sendmail needs to connect to another host or it terminates. Setting it to zero defaults to the old behavior, that is, connections are closed immediately. Since this consumes file descriptors, the connection cache should be kept small: 4 is probably a practical maximum.
[K] The maximum amount of time a cached connection will be permitted to idle without activity. If this time is exceeded, the connection is immediately closed. This value should be small (on the order of ten minutes). Before sendmail uses a cached connection, it always sends a RSET command to check the connection; if this fails, it reopens the connection. This keeps your end from failing if the other end times out. The point of this option is to be a good network neighbor and avoid using up excessive resources on the other end. The default is five minutes.
[no short name] If set to a positive value, allow no more than N incoming daemon connections in a one second period. This is intended to flatten out peaks and allow the load average checking to cut in. Defaults to zero (no limits).
[O] Set server SMTP options. The options are key=value pairs. Known keys are:

Port Name/number of listening port (defaults to "smtp")
Addr Address mask (defaults INADDR_ANY)
Family Address family (defaults to INET)
Listen Size of listen queue (defaults to 10)
SndBufSize Size of TCP send buffer
RcvBufSize Size of TCP receive buffer
The Address mask may be a numeric address in dot notation or a network name.
[no short name] When a message that has 8-bit characters but is not in MIME format is converted to MIME (see the EightBitMode option) a character set must be included in the Content-Type: header. This character set is normally set from the Charset= field of the mailer descriptor. If that is not set, the value of this option is used. If this option is not set, the value unknown-8bit is used.
[u] Set the default userid for mailers to user:group. If group is omitted and user is a user name (as opposed to a numeric user id) the default group listed in the /etc/passwd file for that user is used as the default group. Both user and group may be numeric. Mailers without the S flag in the mailer definition will run as this user. Defaults to 1:1. The value can also be given as a symbolic user name.[19]
[d] Deliver in mode x. Legal modes are:

i Deliver interactively (synchronously)
b Deliver in background (asynchronously)
q Just queue the message (deliver during queue run)
d Defer delivery and all map lookups (deliver during queue run)
Defaults to ``b'' if no option is specified, ``i'' if it is specified but given no argument (i.e., ``Od'' is equivalent to ``Odi''). The -v command line flag sets this to i.
[no short name] Dial-on-demand network connections can see timeouts if a connection is opened before the call is set up. If this is set to an interval and a connection times out on the first connection being attempted sendmail will sleep for this amount of time and try again. This should give your system time to establish the connection to your service provider. Units default to seconds, so DialDelay=5 uses a five second delay. Defaults to zero (no retry).
[no short name] The standards say that all host addresses used in a mail message must be fully canonical. For example, if your host is named Cruft.Foo.ORG and also has an alias of FTP.Foo.ORG, the former name must be used at all times. This is enforced during host name canonification ($[ ... $] lookups). If this option is set, the protocols are ignored and the wrong thing is done. However, the IETF is moving toward changing this standard, so the behaviour may become acceptable. Please note that hosts downstream may still rewrite the address to be the true canonical name however.
[no short name] If set, sendmail will avoid using the initgroups(3) call. If you are running NIS, this causes a sequential scan of the groups.byname map, which can cause your NIS server to be badly overloaded in a large domain. The cost of this is that the only group found for users will be their primary group (the one in the password file), which will make file access permissions somewhat more restrictive. Has no effect on systems that don't have group lists.
[R] Normally, sendmail tries to eliminate any unnecessary explicit routes when sending an error message (as discussed in RFC 1123 § 5.2.6). For example, when sending an error message to
sendmail will strip off the @known1,@known2 in order to make the route as direct as possible. However, if the R option is set, this will be disabled, and the mail will be sent to the first address in the route, even if later addresses are known. This may be useful if you are caught behind a firewall.
[no short name] If an error occurs when sending an error message, send the error report (termed a double bounce because it is an error bounce that occurs when trying to send another error bounce) to the indicated address. If not set, defaults to postmaster.
[8] Set handling of eight-bit data. There are two kinds of eight-bit data: that declared as such using the BODY=8BITMIME ESMTP declaration or the -B8BITMIME command line flag, and undeclared 8-bit data, that is, input that just happens to be eight bits. There are three basic operations that can happen: undeclared 8-bit data can be automatically converted to 8BITMIME, undeclared 8-bit data can be passed as-is without conversion to MIME (``just send 8''), and declared 8-bit data can be converted to 7-bits for transmission to a non-8BITMIME mailer. The possible actions are:

[E] Prepend error messages with the indicated message. If it begins with a slash, it is assumed to be the pathname of a file containing a message (this is the recommended setting). Otherwise, it is a literal message. The error file might contain the name, email address, and/or phone number of a local postmaster who could provide assistance in to end users. If the option is missing or null, or if it names a file which does not exist or which is not readable, no message is printed.
[e] Dispose of errors using mode x. The values for x are:
p Print error messages (default)
q No messages, just give exit status
m Mail back errors
w Write back errors (mail if user not logged in)
e Mail back errors and give zero exit stat always
[V] If specified, the fallbackhost acts like a very low priority MX on every host. This is intended to be used by sites with poor network connectivity.
[Y] If set, deliver each job that is run from the queue in a separate process. Use this option if you are short of memory, since the default tends to consume considerable amounts of memory while the queue is being processed.
[J] Set the path for searching for users' .forward files. The default is $z/.forward. Some sites that use the automounter may prefer to change this to /var/forward/$u to search a file with the same name as the user in a system directory. It can also be set to a sequence of paths separated by colons; sendmail stops at the first file it can successfully and safely open. For example, /var/forward/$u:$z/.forward will search first in /var/forward/ username and then in ~username/.forward (but only if the first file does not exist).
[H] Specify the help file for SMTP.
[c] If an outgoing mailer is marked as being expensive, don't connect immediately. This requires that queueing be compiled in, since it will depend on a queue run process to actually send the mail.
[no short name] The path to the hosts database, normally /etc/hosts. This option is only consulted when sendmail is canonifying addresses, and then only when files is in the hosts service switch entry. In particular, this file is never used when looking up host addresses; that is under the control of the system gethostbyname(3) routine.
[no short name] The location of the long term host status information. When set, information about the status of hosts (e.g., host down or not accepting connections) will be shared between all sendmail processes; normally, this information is only held within a single queue run. This option requires a connection cache of at least 1 to function. If the option begins with a leading `/', it is an absolute pathname; otherwise, it is relative to the mail queue directory. A suggested value for sites desiring persistent host status is .hoststat (i.e., a subdirectory of the queue directory).
[i] Ignore dots in incoming messages. This is always disabled (that is, dots are always accepted) when reading SMTP mail.
[L] Set the default log level to n. Defaults to 9.
[no long version] Set the macro x to value. This is intended only for use from the command line. The -M flag is preferred.
[G] Allow fuzzy matching on the GECOS field. If this flag is set, and the usual user name lookups fail (that is, there is no alias with this name and a getpwnam fails), sequentially search the password file for a matching entry in the GECOS field. This also requires that MATCHGECOS be turned on during compilation. This option is not recommended.
[no short name] If set, sendmail will refuse connections when it has more than N children processing incoming mail. This does not limit the number of outgoing connections. If not set, there is no limit to the number of children -- that is, the system load averaging controls this.
[h] The maximum hop count. Messages that have been processed more than N times are assumed to be in a loop and are rejected. Defaults to 25.
[no short name] Not yet implemented. This option specifies how long host status information will be retained. For example, if a host is found to be down, connections to that host will not be retried for this interval. The units default to minutes.
[no short name] Specify the maximum message size to be advertised in the ESMTP EHLO response. Messages larger than this will be rejected.
[no short name] The maximum number of jobs that will be processed in a single queue run. If not set, there is no limit on the size. If you have very large queues or a very short queue run interval this could be unstable. However, since the first N jobs in queue directory order are run (rather than the N highest priority jobs) this should be set as high as possible to avoid losing jobs that happen to fall late in the queue directory.
[m] Send to me too, even if I am in an alias expansion.
[b] Insist on at least N blocks free on the filesystem that holds the queue files before accepting email via SMTP. If there is insufficient space sendmail gives a 452 response to the MAIL command. This invites the sender to try again later.
[no short name] Don't process any queued jobs that have been in the queue less than the indicated time interval. This is intended to allow you to get responsiveness by processing the queue fairly frequently without thrashing your system by trying jobs too often. The default units are minutes.
[no short name] Sets the list of characters that must be quoted if used in a full name that is in the phrase part of a ``phrase <address>'' syntax. The default is ``'.''. The characters ``@,;:\e()[]'' are always added to this list.
[no short name] The action to take when you receive a message that has no valid recipient headers (To:, Cc:, Bcc:, or Apparently-To: -- the last included for back compatibility with old sendmails). It can be None to pass the message on unmodified, which violates the protocol, Add-To to add a To: header with any recipients it can find in the envelope (which might expose Bcc: recipients), Add-Apparently-To to add an Apparently-To: header (this is only for back-compatibility and is officially deprecated), Add-To-Undisclosed to add a header To: undisclosed-recipients:; to make the header legal without disclosing anything, or Add-Bcc to add an empty Bcc: header.
[o] Assume that the headers may be in old format, i.e., spaces delimit names. This actually turns on an adaptive algorithm: if any recipient address contains a comma, parenthesis, or angle bracket, it will be assumed that commas already exist. If this flag is not on, only commas delimit names. Headers are always output with commas between the names. Defaults to off.
[$o macro] The list of characters that are considered to be operators, that is, characters that delimit tokens. All operator characters are tokens by themselves; sequences of non-operator characters are also tokens. White space characters separate tokens but are not tokens themselves -- for example, AAA.BBB has three tokens, but AAA BBB has two. If not set, OperatorChars defaults to .:@[]; additionally, the characters ()<>,; are always operators.
[P] If set, copies of error messages will be sent to the named postmaster. Only the header of the failed message is sent. Since most errors are user problems, this is probably not a good idea on large sites, and arguably contains all sorts of privacy violations, but it seems to be popular with certain operating systems vendors. Defaults to no postmaster copies.
[p] Set the privacy options. ``Privacy'' is really a misnomer; many of these are just a way of insisting on stricter adherence to the SMTP protocol. The options can be selected from:

public Allow open access
needmailhelo Insist on HELO or EHLO command before MAIL
needexpnhelo Insist on HELO or EHLO command before EXPN
noexpn Disallow EXPN entirely
needvrfyhelo Insist on HELO or EHLO command before VRFY
novrfy Disallow VRFY entirely
restrictmailq Restrict mailq command
restrictqrun Restrict -q command line flag
noreceipts Don't return success DSNs
goaway Disallow essentially all SMTP status queries
authwarnings Put X-Authentication-Warning: headers in messages
The goaway pseudo-flag sets all flags except restrictmailq and restrictqrun. If mailq is restricted, only people in the same group as the queue directory can print the queue. If queue runs are restricted, only root and the owner of the queue directory can run the queue. Authentication Warnings add warnings about various conditions that may indicate attempts to spoof the mail system, such as using an non-standard queue directory.
[Q] Use the named dir as the queue directory.
[q] Use factor as the multiplier in the map function to decide when to just queue up jobs rather than run them. This value is divided by the difference between the current load average and the load average limit ( QueueLA option) to determine the maximum message priority that will be sent. Defaults to 600000.
[x] When the system load average exceeds LA, just queue messages (i.e., don't try to send them). Defaults to 8.
[no short name] Sets the algorithm used for sorting the queue. Only the first character of the value is used. Legal values are host (to order by the name of the first host name of the first recipient), time (to order by the submission time), and priority (to order by message priority). Host ordering makes better use of the connection cache, but may tend to process low priority messages that go to a single host over high priority messages that go to several hosts; it probably shouldn't be used on slow network links. Time ordering is almost always a bad idea, since it allows large, bulk mail to go out before smaller, personal mail, but may have applicability on some hosts with very fast connections. Priority ordering is the default.
[T] A synonym for Timeout.queuereturn. Use that form instead of the QueueTimeout form.
[I] Set resolver options. Values can be set using + flag and cleared using - flag; the flags can be debug, aaonly, usevc, primary, igntc, recurse, defnames, stayopen, or dnsrch. The string HasWildcardMX (without a + or -) can be specified to turn off matching against MX records when doing name canonifications. N.B. Prior to 8.7, this option indicated that the name server be responding in order to accept addresses. This has been replaced by checking to see if the dns method is listed in the service switch entry for the hosts service.
[no short name] The user parameter may be a user name (looked up in /etc/passwd) or a numeric user id; either form can have :group attached (where group can be numeric or symbolic). If set to a non-zero (non-root) value, sendmail will change to this user id shortly after startup[20]. This avoids a certain class of security problems. However, this means that all .forward and :include: files must be readable by the indicated user, and on systems that don't support the saved uid bit properly, all files to be written must be writable by user and all programs will be executed by user. It is also incompatible with the SafeFileEnvironment option. In other words, it may not actually add much to security on an average system, and may in fact detract from security (because other file permissions must be loosened). However, it should be useful on firewalls and other places where users don't have accounts and the aliases file is well constrained.
[y] The indicated factor is added to the priority (thus lowering the priority of the job) for each recipient, i.e., this value penalizes jobs with large numbers of recipients. Defaults to 30000.
[X] When the system load average exceeds LA, refuse incoming SMTP connections. Defaults to 12.
[Z] The factor is added to the priority every time a job is processed. Thus, each time a job is processed, its priority will be decreased by the indicated value. In most environments this should be positive, since hosts that are down are all too often down for a long time. Defaults to 90000.
[no short name] If this option is set, sendmail will do a chroot(2) call into the indicated directory before doing any file writes. If the file name specified by the user begins with dir, that partial path name will be stripped off before writing, so (for example) if the SafeFileEnvironment variable is set to /safe then aliases of /safe/logs/file and /logs/file actually indicate the same file. Additionally, if this option is set, sendmail refuses to deliver to symbolic links.
[f] Save Unix-style From lines at the front of headers. Normally they are assumed redundant and discarded.
[j] If set, send error messages in MIME format (see RFC1521 and RFC1344 for details). If disabled, sendmail will not return the DSN keyword in response to an EHLO and will not do Delivery Status Notification processing as described in RFC1891.
[no short name] If your host operating system has a service switch abstraction (e.g., /etc/nsswitch.conf on Solaris or /etc/svc.conf on Ultrix and DEC OSF/1) that service will be consulted and this option is ignored. Otherwise, this is the name of a file that provides the list of methods used to implement particular services. The syntax is a series of lines, each of which is a sequence of words. The first word is the service name, and following words are service types. The services that sendmail consults directly are aliases and hosts. Service types can be dns, nis, nisplus, or files (with the caveat that the appropriate support must be compiled in before the service can be referenced). If ServiceSwitchFile is not specified, it defaults to /etc/service.switch. If that file does not exist, the default switch is:
aliases files
hosts dns nis files
The default file is /etc/service.switch.
[7] Strip input to seven bits for compatibility with old systems. This shouldn't be necessary.
[no short name] If set, From: lines that have embedded newlines are unwrapped onto one line. This is to get around a botch in Lotus Notes that apparently cannot understand legally wrapped RFC822 headers.
[no short name] If set, a client machine will never try to open two SMTP connections to a single server machine at the same time, even in different processes. That is, if another sendmail is already talking to some host a new sendmail will not open another connection. This property is of mixed value; although this reduces the load on the other machine, it can cause mail to be delayed (for example, if one sendmail is delivering a huge message, other sendmails won't be able to send even small messages). Also, it requires another file descriptor (for the lock file) per connection, so you may have to reduce the ConnectionCacheSize option to avoid running out of per-process file descriptors. Requires the HostStatusDirectory option.
[$e macro] The message printed when the SMTP server starts up. Defaults to $j Sendmail $v ready at $b.
[S] Log summary statistics in the named file. If not set, no summary statistics are saved. This file does not grow in size. It can be printed using the mailstats(8) program.
[s] Be super-safe when running things, i.e., always instantiate the queue file, even if you are going to attempt immediate delivery. Sendmail always instantiates the queue file before returning control the client under any circumstances. This should really always be set.
[F] The file mode for queue files. It is interpreted in octal by default. Defaults to 0600.
[r; subsumes old T option as well] Set timeout values. The actual timeout is indicated by the type. The recognized timeouts and their default values, and their minimum values specified in RFC 1123 section 5.3.2 are:

initial wait for initial greeting message [5m, 5m]
helo reply to HELO or EHLO command [5m, none]
mail reply to MAIL command [10m, 5m]
rcpt reply to RCPT command [1h, 5m]
datainit reply to DATA command [5m, 2m]
datablock data block read [1h, 3m]
datafinal reply to final ``.'' in data [1h, 10m]
rset reply to RSET command [5m, none]
quit reply to QUIT command [2m, none]
misc reply to NOOP and VERB commands [2m, none]
ident IDENT protocol timeout [30s, none]
fileopen* timeout on opening .forward and :include: files [60s, none]
command* command read [1h, 5m]
queuereturn* how long until a message is returned [5d, 5d]
queuewarn* how long until a warning is sent [none, none]
hoststatus* how long until host status is ``stale'' [30m, none]
All but those marked with a dagger (*) apply to client SMTP. If the message is submitted using the NOTIFY SMTP extension, warning messages will only be sent if NOTIFY=DELAY is specified. The queuereturn and queuewarn timeouts can be further qualified with a tag based on the Precedence: field in the message; they must be one of urgent (indicating a positive non-zero precedence) normal (indicating a zero precedence), or non-urgent (indicating negative precedences). For example, setting Timeout.queuewarn.urgent=1h sets the warning timeout for urgent messages only to one hour. The default if no precedence is indicated is to set the timeout for all precedences.
[t] Set the local time zone info to tzinfo -- for example, PST8PDT. Actually, if this is not set, the TZ environment variable is cleared (so the system default is used); if set but null, the user's TZ variable is used, and if set and non-null the TZ variable is set to this value.
[w] If this system is the best (that is, lowest preference) MX for a given host, its configuration rules should normally detect this situation and treat that condition specially by forwarding the mail to a UUCP feed, treating it as local, or whatever. However, in some cases (such as Internet firewalls) you may want to try to connect directly to that host as though it had no MX records at all. Setting this option causes sendmail to try this. The downside is that errors in your configuration are likely to be diagnosed as host unknown or message timed out instead of something more meaningful. This option is disrecommended.
[$l macro] Defines the format used when sendmail must add a UNIX-style From_ line (that is, a line beginning From<space>user). Defaults to From $g $d. Don't change this unless your system uses a different UNIX mailbox format (very unlikely).
[no short name] If set, :include: and .forward files that are group writable are considered unsafe, that is, they cannot reference programs or write directly to files. World writable :include: and .forward files are always unsafe..
[l] If there is an Errors-To: header, send error messages to the addresses listed there. They normally go to the envelope sender. Use of this option causes sendmail to violate RFC 1123. This option is disrecommended and deprecated.
[U] The user database specification.
[no short name] This is an initial submission directly from a Mail User Agent. This can be set in the configuration file if you have MUAs that don't pass the -U flag or use the XUSR ESMTP extension, but some relayed mail may get inappropriately rewritten if you do.
[v] Run in verbose mode. If this is set, sendmail adjusts options HoldExpensive (old c) and DeliveryMode (old d) so that all mail is delivered completely in a single job so that you can see the entire delivery process. Option Verbose should never be set in the configuration file; it is intended for command line use only.

All options can be specified on the command line using the -O or -o flag, but most will cause sendmail to relinquish its setuid permissions. The options that will not cause this are MinFreeBlocks [b], DeliveryMode [d], ErrorMode [e], IgnoreDots [i], LogLevel [L], MeToo [m], OldStyleHeaders [o], PrivacyOptions [p], Timeouts [r], SuperSafe [s], Verbose [v], CheckpointInterval [C], and SevenBitInput [7]. Also, M (define macro) when defining the r or s macros is also considered safe.

P -- Precedence Definitions

Values for the Precedence: field may be defined using the P control line. The syntax of this field is:

When the name is found in a Precedence: field, the message class is set to num. Higher numbers mean higher precedence. Numbers less than zero have the special property that if an error occurs during processing the body of the message will not be returned; this is expected to be used for bulk mail such as through mailing lists. The default precedence is zero. For example, our list of precedences is:
People writing mailing list exploders are encouraged to use Precedence: list. Older versions of sendmail (which discarded all error returns for negative precedences) didn't recognize this name, giving it a default precedence of zero. This allows list maintainers to see error returns on both old and new versions of sendmail.

V -- Configuration Version Level

To provide compatibility with old configuration files, the V line has been added to define some very basic semantics of the configuration file. These are not intended to be long term supports; rather, they describe compatibility features which will probably be removed in future releases.

N.B.: these version levels have nothing to do with the version number on the files. For example, as of this writing version 8 config files (specifically, 8.7) used version level 6 configurations.

Old configuration files are defined as version level one. Version level two files make the following changes:

  1. Host name canonification ($[ ... $]) appends a dot if the name is recognized; this gives the config file a way of finding out if anything matched. (Actually, this just initializes the host map with the -a. flag -- you can reset it to anything you prefer by declaring the map explicitly.)
  2. Default host name extension is consistent throughout processing; version level one configurations turned off domain extension (that is, adding the local domain name) during certain points in processing. Version level two configurations are expected to include a trailing dot to indicate that the name is already canonical.
  3. Local names that are not aliases are passed through a new distinguished ruleset five; this can be used to append a local relay. This behaviour can be prevented by resolving the local name with an initial `@'. That is, something that resolves to a local mailer and a user name of vikki will be passed through ruleset five, but a user name of @vikki will have the `@' stripped, will not be passed through ruleset five, but will otherwise be treated the same as the prior example. The expectation is that this might be used to implement a policy where mail sent to vikki was handled by a central hub, but mail sent to vikki@localhost was delivered directly.

Version level three files allow # initiated comments on all lines. Exceptions are backslash escaped # marks and the $# syntax.

Version level four configurations are completely equivalent to level three for historical reasons.

Version level five configuration files change the default definition of $w to be just the first component of the hostname.

Version level six configuration files change many of the local processing options (such as aliasing and matching the beginning of the address for `|' characters) to be mailer flags; this allows fine-grained control over the special local processing. Level six configuration files may also use long option names. The ColonOkInAddr option (to allow colons in the local-part of addresses) defaults on for lower numbered configuration files; the configuration file requires some additional intelligence to properly handle the RFC 822 group construct.

The V line may have an optional / vendor to indicate that this configuration file uses modifications specific to a particular vendor[21]. You may use /Berkeley to emphasize that this configuration file uses the Berkeley dialect of sendmail.

K -- Key File Declaration

Special maps can be defined using the line:

Kmapname mapclass arguments
The mapname is the handle by which this map is referenced in the rewriting rules. The mapclass is the name of a type of map; these are compiled in to sendmail. The arguments are interpreted depending on the class; typically, there would be a single argument naming the file containing the map.

Maps are referenced using the syntax:

$( map key $@ arguments $: default $)
where either or both of the arguments or default portion may be omitted. The $@ arguments may appear more than once. The indicated key and arguments are passed to the appropriate mapping function. If it returns a value, it replaces the input. If it does not return a value and the default is specified, the default replaces the input. Otherwise, the input is unchanged.

The arguments are passed to the map for arbitrary use. Most map classes can interpolate these arguments into their values using the syntax %n (where n is a digit) to indicate the corresponding argument. Argument %0 indicates the database key. For example, the rule

R$- ! $+ $: $(uucp $1 $@ $2 $: %1 @ %0 . UUCP $)
Looks up the UUCP name in a (user defined) UUCP map; if not found it turns it into .UUCP form. The database might contain records like:
decvax %1@%0.DEC.COM
research %1@%0.ATT.COM
Note that default clauses never do this mapping.

The built in map with both name and class host is the host name canonicalization lookup. Thus, the syntax:

$(host hostname$)
is equivalent to:

There are many defined classes.

Database lookups using the ndbm(3) library. Sendmail must be compiled with NDBM defined.
Database lookups using the btree interface to the Berkeley db(3) library. Sendmail must be compiled with NEWDB defined.
Database lookups using the hash interface to the Berkeley db(3) library. Sendmail must be compiled with NEWDB defined.
NIS lookups. Sendmail must be compiled with NIS defined.
NIS+ lookups. Sendmail must be compiled with NISPLUS defined. The argument is the name of the table to use for lookups, and the -k and -v flags may be used to set the key and value columns respectively.
Hesiod lookups. Sendmail must be compiled with HESIOD defined.
LDAP X500 directory lookups. Sendmail must be compiled with LDAPMAP defined. The map supports most of the standard arguments and most of the command line arguments of the ldapsearch program.
NeXT NetInfo lookups. Sendmail must be compiled with NETINFO defined.
Text file lookups. The format of the text file is defined by the -k (key field number), -v (value field number), and -z (field delimiter) flags.
Internal symbol table lookups. Used internally for aliasing.
Really should be called alias -- this is used to get the default lookups for alias files, and is the default if no class is specified for alias files.
Looks up users using getpwnam(3). The -v flag can be used to specify the name of the field to return (although this is normally used only to check the existence of a user).
Canonifies host domain names. Given a host name it calls the name server to find the canonical name for that host.
The arguments on the `K' line are a list of maps; the resulting map searches the argument maps in order until it finds a match for the indicated key. For example, if the key definition is:
Kmap1 ...
Kmap2 ...
Kseqmap sequence map1 map2
then a lookup against seqmap first does a lookup in map1. If that is found, it returns immediately. Otherwise, the same key is used for map2.
Much like the sequence map except that the order of maps is determined by the service switch. The argument is the name of the service to be looked up; the values from the service switch are appended to the map name to create new map names. For example, consider the key definition:
Kali switch aliases
together with the service switch entry:
aliases nis files
This causes a query against the map ali to search maps named ali.nis and ali.files in that order.
Strip double quotes (") from a name. It does not strip backslashes, and will not strip quotes if the resulting string would contain unscannable syntax (that is, basic errors like unbalanced angle brackets; more sophisticated errors such as unknown hosts are not checked). The intent is for use when trying to accept mail from systems such as DECnet that routinely quote odd syntax such as
A typical usage is probably something like:
Kdequote dequote


R$- $: $(dequote $1 $)
R$- $+ $: $>3 $1 $2

Care must be taken to prevent unexpected results; for example,
"|someprogram < input > output"
will have quotes stripped, but the result is probably not what you had in mind. Fortunately these cases are rare.

Most of these accept as arguments the same optional flags and a filename (or a mapname for NIS; the filename is the root of the database path, so that .db or some other extension appropriate for the database type will be added to get the actual database name). Known flags are:

Indicates that this map is optional -- that is, if it cannot be opened, no error is produced, and sendmail will behave as if the map existed but was empty.
-N, -O
If neither -N or -O are specified, sendmail uses an adaptive algorithm to decide whether or not to look for null bytes on the end of keys. It starts by trying both; if it finds any key with a null byte it never tries again without a null byte and vice versa. If -N is specified it never tries without a null byte and if -O is specified it never tries with a null byte. Setting one of these can speed matches but are never necessary. If both -N and -O are specified, sendmail will never try any matches at all -- that is, everything will appear to fail.
Append the string x on successful matches. For example, the default host map appends a dot on successful matches.
Do not fold upper to lower case before looking up the key.
Match only (without replacing the value). If you only care about the existence of a key and not the value (as you might when searching the NIS map hosts.byname for example), this flag prevents the map from substituting the value. However, The -a argument is still appended on a match, and the default is still taken if the match fails.
The key column name (for NIS+) or number (for text lookups). For LDAP maps this is a filter string passed to printf with a %s where the string to be mapped is inserted.
The value column name (for NIS+) or number (for text lookups). For LDAP maps this is the name of the attribute to be returned.
The column delimiter (for text lookups). It can be a single character or one of the special strings \en or \et to indicate newline or tab respectively. If omitted entirely, the column separator is any sequence of whitespace.
Normally, when a map attempts to do a lookup and the server fails (e.g., sendmail couldn't contact any name server; this is not the same as an entry not being found in the map), the message being processed is queued for future processing. The -t flag turns off this behaviour, letting the temporary failure (server down) act as though it were a permanent failure (entry not found). It is particularly useful for DNS lookups, where someone else's misconfigured name server can cause problems on your machine. However, care must be taken to ensure that you don't bounce mail that would be resolved correctly if you tried again. A common strategy is to forward such mail to another, possibly better connected, mail server.
For the dequote map only, the character to use to replace space characters after a successful dequote.

The dbm map appends the strings .pag and .dir to the given filename; the two db-based maps append .db. For example, the map specification

Kuucp dbm -o -N /usr/lib/uucpmap
specifies an optional map named uucp of class dbm; it always has null bytes at the end of every string, and the data is located in /usr/lib/uucpmap.{dir,pag}.

The program makemap(8) can be used to build any of the three database-oriented maps. It takes the following flags:

Do not fold upper to lower case in the map.
Include null bytes in keys.
Append to an existing (old) file.
Allow replacement of existing keys; normally, re-inserting an existing key is an error.
Print what is happening.

The sendmail daemon does not have to be restarted to read the new maps as long as you change them in place; file locking is used so that the maps won't be read while they are being updated.[22]

New classes can be added in the routine setupmaps in file conf.c.

The User Database

If you have a version of sendmail with the user database package compiled in, the handling of sender and recipient addresses is modified.

The location of this database is controlled with the UserDatabaseSpec option.

Structure of the user database

The database is a sorted (BTree-based) structure. User records are stored with the key:

The sorted database format ensures that user records are clustered together. Meta-information is always stored with a leading colon.

Field names define both the syntax and semantics of the value. Defined fields include:

The delivery address for this user. There may be multiple values of this record. In particular, mailing lists will have one maildrop record for each user on the list.
The outgoing mailname for this user. For each outgoing name, there should be an appropriate maildrop record for that name to allow return mail. See also :default:mailname.
Changes any mail sent to this address to have the indicated envelope sender. This is intended for mailing lists, and will normally be the name of an appropriate -request address. It is very similar to the owner- list syntax in the alias file.
The full name of the user.
The office address for this user.
The office phone number for this user.
The office FAX number for this user.
The home address for this user.
The home phone number for this user.
The home FAX number for this user.
A (short) description of the project this person is affiliated with. In the University this is often just the name of their graduate advisor.
A pointer to a file from which plan information can be gathered.

As of this writing, only a few of these fields are actually being used by sendmail: maildrop and mailname. A finger program that uses the other fields is planned.

User database semantics

When the rewriting rules submit an address to the local mailer, the user name is passed through the alias file. If no alias is found (or if the alias points back to the same address), the name (with :maildrop appended) is then used as a key in the user database. If no match occurs (or if the maildrop points at the same address), forwarding is tried.

If the first token of the user name returned by ruleset 0 is an @ sign, the user database lookup is skipped. The intent is that the user database will act as a set of defaults for a cluster (in our case, the Computer Science Division); mail sent to a specific machine should ignore these defaults.

When mail is sent, the name of the sending user is looked up in the database. If that user has a mailname record, the value of that record is used as their outgoing name. For example, I might have a record:

eric:mailname Eric.Allman@CS.Berkeley.EDU
This would cause my outgoing mail to be sent as Eric.Allman.

If a maildrop is found for the user, but no corresponding mailname record exists, the record :default:mailname is consulted. If present, this is the name of a host to override the local host. For example, in our case we would set it to CS.Berkeley.EDU. The effect is that anyone known in the database gets their outgoing mail stamped as user@CS.Berkeley.EDU, but people not listed in the database use the local hostname.



The user database is built from a text file using the makemap utility (in the distribution in the makemap subdirectory). The text file is a series of lines corresponding to userdb records; each line has a key and a value separated by white space. The key is always in the format described above -- for example:

This file is normally installed in a system directory; for example, it might be called /etc/userdb. To make the database version of the map, run the program:
makemap btree /etc/userdb.db < /etc/userdb
Then create a config file that uses this. For example, using the V8 M4 configuration, include the following line in your .mc file:
define(`confUSERDB_SPEC', /etc/userdb.db)

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Claus Aßmann Please send comments to: <>