HP-UX Mailing Services Administrator's Guide

Sendmail 8.13.3
Overview
Chapter 3 109
Overview
Sendmail 8.13.3 is the latest version of Web upgrade available on the
HP-UX 11i v1 and HP-UX 11i v2 operating systems at
http://www.software.hp.com.
The main difference between Sendmail 8.11.1 and Sendmail 8.13.3 is
that Sendmail 8.13.3 can act as a Mail Submission Program (MSP) using
a different configuration file compared to the one used by the Sendmail
daemon MTA. The /etc/mail/submit.cf file is the default Sendmail
MSP configuration file.
When Sendmail starts up in the daemon mode, it listens both on the
normal port 25 for incoming SMTP connections and on port 587 for the
local submission of mail. The latter role is that of an MSA (documented
in RFC 2476) and requires that Mail User Agents (MUAs) be explicitly
coded to use port 587 for local submission of mail directly to the
Sendmail daemon.
NOTE The role of the Sendmail daemon as an MSA (introduced on 8.11.1) is a
different concept from that of the role of Sendmail as an MSP.
When Sendmail 8.13.3 is executed independently or invoked from a MUA
to process locally submitted mail, Sendmail takes on the role of an MSP.
MSP accepts and processes the submitted mail messages as a non-root
user and queues them separately. After processing, MSP delivers the
submitted mail messages to the Sendmail MTA daemon using the SMTP
protocol through the port 25. The default /etc/mail/submit.cf file
assumes that the MTA sendmail daemon is running on the local host.
When the Sendmail MTA is started, by default an additional Sendmail
MSP queue-processing daemon is also started. The MSP queue daemon
does not listen on any socket. The only purpose of the MSP queue
daemon is to periodically scan the MSP mail queues for any mail
messages accepted by MSP which have not yet been forwarded to the
Sendmail MTA daemon.