Message Submission Agent (MSA)
- Based on RFC 2476: Message Submission
- SMTP protocol over port 587 (instead of normal 25)
- Meant to be less strict on standards compliance
- Addresses don't have to be fully qualified
- Hostnames don't have to be fully qualified
- Don't require "required" headers, e.g.
Message-ID: and
Date:
- MSA brings message into standards compliance before relaying to an MTA
- MSA port should be limited to internal hosts (e.g., firewalled from
external world)
- sendmail MTA has always been forgiving in what it accepts and strict in
what it sends.
- Historically, port 25 has acted as both an MTA and MSA port in sendmail
- Future versions may make port 25 more strict
- MSA port employs different features
- Doesn't allow ETRN
- May require SMTP Authentication
- Accomplished through new
DaemonPortOptions
(DAEMON_OPTIONS()) syntax
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