Linux – Postfix and Sendmail smmsp cron job

linuxsendmailUbuntu

I'm running Ubuntu 13.10 and have recently replaced the default Sendmail installation with Postfix. From what I've read elsewhere Ubuntu requires Sendmail for system functions so Postfix emulates the sendmail submission program.

I've recently noticed the following in /var/log/mail.log occurring every 20 mins:

Jan 28 15:00:01 domain postfix/pickup[2452]: 2F81583C8B: uid=108 from=<smmsp>
Jan 28 15:00:01 domain postfix/cleanup[2765]: 2F81583C8B: message-id=<20140128150001.2F81583C8B@domain.co.uk>
Jan 28 15:00:01 domain postfix/qmgr[1881]: 2F81583C8B: from=<smmsp@domain.co.uk>, size=684, nrcpt=1 (queue active)
Jan 28 15:00:06 domain postfix/smtp[2767]: 2F81583C8B: to=<root@domain.co.uk>, orig_to=<root>, relay=mail.domain.co.uk[79.170.40.74]:25, delay=5.4, delays=0.01/0.01/5.3/0.05, dsn=5.0.0, status=bounced (host mail.domain.co.uk[79.170.4$
Jan 28 15:00:06 domain postfix/cleanup[2765]: 87F9F83C8C: message-id=<20140128150006.87F9F83C8C@domain.co.uk>
Jan 28 15:00:06 domain postfix/qmgr[1881]: 87F9F83C8C: from=<>, size=2663, nrcpt=1 (queue active)
Jan 28 15:00:06 domain postfix/bounce[2768]: 2F81583C8B: sender non-delivery notification: 87F9F83C8C
Jan 28 15:00:06 domain postfix/qmgr[1881]: 2F81583C8B: removed
Jan 28 15:00:06 domain postfix/smtp[2767]: 87F9F83C8C: to=<smmsp@domain.co.uk>, relay=mail.domain.co.uk[79.170.40.74]:25, delay=0.28, delays=0/0/0.24/0.03, dsn=5.0.0, status=bounced (host mail.domain.co.uk[79.170.40.74] said: 550 unk$
Jan 28 15:00:06 domain postfix/qmgr[1881]: 87F9F83C8C: removed

I understand that smmsp is the sendmail user and I can trace this back to a cron job in /etc/cron.d/sendmail. Now that I'm running postfix and not sendmail do I still need this cron job to run, or can I just comment it out?

Best Answer

For the benefit of future readers searching for smmsp on Server Fault:

smmsp

The smmsp (SendMail Message Submission Program) user and group are specific to the Sendmail package and are not used by Postfix – or any other Mail Transfer Agent (MTA).

smmsp is the default user that Sendmail uses if you haven’t configured a specific non-root user for the sendmail command to run as. It was introduced as a security measure so that vulnerabilities in sendmail couldn’t provide an exploiter with root access to the system.

From the Sendmail Installation and Operation Guide

The binary for sendmail is located in /usr/sbin. It should be set-group-ID smmsp

See also Add smmsp to /etc/passwd from Sendmail, 4th Edition (O’Reilly).

Checking for / Removing Sendmail

From the information provided in the question, both Postfix and Sendmail are installed (and running) simultaneously. This can be verified by running,

dpkg -l | grep sendmail

To avoid conflict between the two MTAs, remove the Sendmail package(s) listed by the previous command.

It seems that many other users who thought that they’d removed Sendmail had, in fact, only uninstalled the sendmail-base and sendmail packages so they had to remove the following packages:

aptitude purge sendmail-bin sendmail-cf sendmail-doc

Here's a related post from another user who thought that they had uninstalled Sendmail from their system: Postfix/Sendmail: Frequent emails from smmsp to root.

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