Hi Mark,
For the answer.
Are there entries for the messages in Mailman's 'smtp' and 'post' logs?
Presumably, there are not entries in Mailman's 'smtp-failure' log since you say "I don't find any errors on neither the postfix nor the mailman logs"
There are a few possibilities. The first that comes to mind is OutgoingRunner is not running and the messages are still queued in Mailman's out/ queue (this could be /usr/local/mailman/qfiles/out/, /var/lib/mailman/qfiles/out/. /var/spool/mailman/out/ or elsewhere depending on how Mailman was installed).
Actually the emails finally went out, it just takes them a few hours (probably more last week) to be processed. Regarding mailman's queue, I still have to read the documentation to understand how it works because I remember checking this queue but didn't see a lot of files. Is it that, if I send an email to a list with 11000 members, only one file is created there?
As it seems now to be a tuning problem, I started having a look at the mailman's wiki page on performance tuning. Reference is made there to QRUNNER_LOCK_LIFETIME, QRUNNER_PROCESS_LIFETIME, and QRUNNER_MAX_MESSAGES. I did a grep on my mailman's installation but did not find them (I've mailman 2.1.13). Knowing that I host +/- 50 mailing lists, most of them small (3'/40 users) but a few with between 2000 and 11700 users, I'm trying to understand what I can do to improve the tuning.
I will also have a look later at postfix's configuration (I will anyway have to do something there because both yahoo and hotmail are slowing us, temporarily refusing the connection) but the fact is that these emails I was waiting for were not in postfix's queue.
Kind regards,
Gaël