Long-time Postfix user, since the days of version 1. I have a server that is running Mailman on a CentOS 7 machine. Mailman has a couple lists that have quite a few digest users, so once a day, a blast of a bit under 1k messages go out. Have been running this for quite some time with really no issues.
However, lately, I got a complaint from a user who was not getting the Mailman digest. Mailman is set to personalize all messages, so it is not grouping any emails. I looked at the logs, and saw that indeed, a message was generated to the user, but Postfix never shows it being delivered.
When a message is sent individually, I see the following logs:
May 12 01:30:06 lists postfix/smtpd: DF1AC535BB: client=localhost[127.0.0.1]
May 12 01:30:06 lists postfix/cleanup: DF1AC535BB: message-id=<[hidden email]>
May 12 01:30:06 lists postfix/qmgr: DF1AC535BB: from=<sac-bounces+user=[hidden email]>, size=6154, nrcpt=1 (queue active)
May 12 01:30:17 lists postfix/smtp: DF1AC535BB: to=<[hidden email]>, relay=cloudmail102.zonecybersite.com[126.96.36.199]:25, delay=11, delays=0.02/0/1.1/9.9, dsn=2.0.0, status=sent (250 OK)
May 12 01:30:17 lists postfix/qmgr: DF1AC535BB: removed
But more typically, I see only this:
May 13 01:30:06 lists postfix/smtpd: 2D7D7185A2: client=localhost[127.0.0.1]
May 13 01:30:06 lists postfix/cleanup: 2D7D7185A2: message-id=<[hidden email]>
May 13 01:30:06 lists postfix/qmgr: 2D7D7185A2: from=<sac-bounces+user=[hidden email]>, size=14168, nrcpt=1 (queue active)
There is never a "sent" line, nor a "removed" line. In the above example, there is never any more references to 2D7D7185A2 in the rest of the log, nor is there anything in any of the queues. mailq does not show this message, neither does a check for the 2D7D file exist anywhere on the file system. Grepping thru the log also shows no other contact to the zonecybersite.com mailserver. There are no blocks in the firewall that would affect this. Again, if I send a message not during the big blast of digests, it goes thru fine. There's gigs and gigs of free disk space. I don't see any indications of insufficient memory, nor have I any other reports of missing mail delivery.
I am running postfix from the Centos RPM: postfix-2.10.1-9.el7.x86_64