Resolved Inbound Mail Stays in Queue

[Dan Hammer]

This is a new problem for me. This is a new server running Plesk (not my first Plesk system) and I have a problem where inbound mail stays in queue. I've attempted to flush the queue and no luck. I've done the mailbox repair command from the command line with no luck. I've checked DNS settings and those seem fine. The entries in /var/log/maillog are rather generic as well. No permission denied errors or anything along those lines.

This is what I get....

Oct 6 18:40:10 web1 postfix/pipe[966]: A1DA120005B14: to=<user@example.com>, relay=plesk_virtual, delay=553, delays=553/0.03/0/0.13, dsn=4.2.1, status=deferred (Message can not be delivered at this time )

I'd like to add that I've disabled and re-enabled the mailbox as well with no change in results.

The machine is running CentOS 7.5.1804 and Plesk Onyx 17.8.11 Update #24.

I've tried everything I can think of but I am just out of ideas. I would like to add that I get the following warning in the maillog. It may or may not have anything to do with this problem.

Oct 6 18:34:20 web1 dovecot: master: Warning: fd limit (ulimit -n) is lower than required under max. load (1024 < 2500), because of default_client_limit

 

[Dan Hammer]

I managed to get the warning fixed but mail will still not deliver (inbound). Outbound mail works. Is there any chance this could be a firewall related issue? Or some kind of security feature?

 

[Dan Hammer]

After hours of trial and error (mostly error), I stumbled across the solution. I tried disabling the firewall just in case but that didn't work. I tried disabling Spamassassin but no change. I decided to change the SMTP server from Postfix to Qmail to see if that would work. I tried another test mail and this one arrived. So is seemed Postfix was the problem. I wanted to do one more test. I switched back to Postfix and sent another test mail. This one finally arrived. The best I can tell is something in the initial Postfix install may have been nerfed. The reinstall seemed to fix whatever the issue was.

I went to Tools & Settings -> Plesk -- Updates and Upgrades. From there I selected Add/Remove Components. I went to "Mail hosting" (expanded) -- to SMTP Servers -- switched from Postfix to Qmail and selected "Continue". After the process ran I simply repeated those steps and switched back to Postfix. Problem solved.

 

[TorbHo]

Next time, try to disable apparmor and than flush mailqueue (postqueue -f): How to disable AppArmor on Plesk 12.x

That solved the problem for me.
Please keep in mind, that apparmor is part of Plesk Onyx since 17.0 and should not be uninstalled completely.