Site stops sending emails after OS upgrade

Hi everyone,
A friend of mine has this problem with her elgg-based site on Debian 11. She has already posted to a forum on elgg.org site, but somehow I think this is more a server configuration issue. When I look at the logs, it looks like elgg delivers the message to postfix but then the email is not sent, internally bouncing instead.
OS: Debian 11.11 (Kernel: Linux 5.10.0-33-amd64 Architecture:x86-64)
HTTP server: Apache v2.4.62
ISPConfig 3.2.12p1
PHP v7.0 specified for this site on ISPConfig. Also tried with PHPv7.4 which seems to be the higest compatible PHP version for the Elgg version.
Elgg v2.3.12

Below is the description of the problem:
After the recent OS upgrade from Debian 10 to Debian 11 along with the ISPConfig upgrade, the site can no longer send generated emails. Emails which are automatically created as a result of the user actions like `likes`, `friend requests` etc. Still send and receive emails via roundcube at the same domain though.

Using own server for sending emails. The email setup is postfix, lmtp, dovecot

This is the relevant lines from /var/log/mail.log after a typical unsuccessful (internally) bounced email:

pr 1 21:30:20 sunucu postfix/master[38137]: daemon started -- version 3.5.25, configuration /etc/postfix
Apr 1 21:30:24 sunucu postfix/smtps/smtpd[38145]: connect from unknown[81.30.107.119]
Apr 1 21:30:36 sunucu postfix/pickup[38138]: 2048F6E3A9D: uid=5013 from=<webmaster@mydomain.com>
Apr 1 21:30:36 sunucu postfix/cleanup[38157]: 2048F6E3A9D: message-id=<20250401193036.2048F6E3A9D@mail.mydomain.com>
Apr 1 21:30:36 sunucu opendkim[1094]: 2048F6E3A9D: DKIM-Signature field added (s=kersts, d=mydomain.com)
Apr 1 21:30:36 sunucu postfix/qmgr[38139]: 2048F6E3A9D: from=<webmaster@mydomain.com>, size=409, nrcpt=1 (queue active)
Apr 1 21:30:36 sunucu postfix/smtpd[38160]: connect from localhost[127.0.0.1]
Apr 1 21:30:36 sunucu postfix/lmtp[38159]: 2048F6E3A9D: to=<info@mydomain.com>, relay=127.0.0.1[127.0.0.1]:10025, delay=0.13, delays=0.07/0.02/0.04/0,
dsn=5.5.2, status=bounced (host 127.0.0.1[127.0.0.1] refused to talk to me: 502 5.5.2 Error: command not recognized)
Apr 1 21:30:36 sunucu postfix/smtpd[38160]: disconnect from localhost[127.0.0.1] quit=1 unknown=0/1 commands=1/2
Apr 1 21:30:36 sunucu postfix/cleanup[38157]: 3F2946E3A9E: message-id=<20250401193036.3F2946E3A9E@mail.mydomain.com>
Apr 1 21:30:36 sunucu postfix/bounce[38161]: 2048F6E3A9D: sender non-delivery notification: 3F2946E3A9E sunucu
Apr 1 21:30:36 postfix/qmgr[38139]: 3F2946E3A9E: from=<>, size=3075, nrcpt=1 (queue active)

As far as I can see, it fails when postfix tries to send the email via lmtp (presumably to dovecot). What I do not understand it, I thought postfix used lmtp only for incoming emails and when passing them to dovecot, Whereas this is an outgoing email and I would expect lmtp not to be used and instead it to use smtp.
I appreciate any help please!
Best.

 

Hi,
I have been trying out things. I have updated the port number in following from 10025 to 10026:
in Amavis user-50: $forward_method = 'smtp:[127.0.0.1]:10026';
in Postfix master.cf: 127.0.0.1:10026 inet n - n - - smtpd
But regardless, Amavis is still trying to connect to port 10025 for Postfix.
Any ideas what might be overriding these settings?
I appreciate any help please!
Best.

 

Thank you for your reply!
From the person:
"
I have followed the following in this order:
1- https://www.howtoforge.com/how-to-upgrade-from-debian-10-to-debian-11/
2- https://www.howtoforge.com/update-the-ispconfig-perfect-server-from-debian-10-to-debian-11/
3- https://www.howtoforge.com/ispconfig-php-debian/

It is possible that I have overlooked something in steps 2 and 3. Is there a way to check if updates were run properly? Or should I rerun steps 2 and 3?
"
Thank you again for your reply!
Best.

 

Hi,
Looks like indeed the issue was neatly resolved by simply rerunning the ISPConfig upgrade again. Below is her folllowup to the issue on Elgg community site over her experience:
https://elgg.org/discussion/view/3333170/site-cannot-send-automatically-generated-emails
Thanks for the help.
Best.