Intermittent email outage at one location

Virtualmin running on Ubuntu 20.04.1 LTS.

At one office location I have some 20+ users using mail clients (Thunderbird / Outlook) to connect to their mail at mail.mydomain.com. Each user has between 1 and 5 mail accounts, and some of the users are connected to shared mail accounts like “application@” “scheduling@” etc… A few times a day, the connection to the mail server is blocked. The users have their messages hang in outbox, and 5-10 minutes later everything goes back to normal. This affects all users at the location every time it happens and users who switch to cellphone hotspot immediately regain connection, I want to assume this is related to some kind of connection limit, but if there’s a setting to set higher I sure cant find it.

Virtualmin/Ubuntu is installed Bare-Metal on an 8 core system @ 3.2Ghz with 32 GB ram, so if there is need for limit increases, I should have plenty of power as I am still way above the recommended system specs for Virtualmin.

I’m standing by for any follow-up questions and would really appreciate any help, this is starting to make me look real bad, as I am a solo front end developer. :frowning:

I’m willing to bet a kidney that one of those users has one device connecting with a wrong user/pass combo making the server ban that IP for a limited time.
Pretty common in an shared office environment like that.

Edit: check the logs for failed login attempts.

2 Likes

Doing so now, that would be legendary.

I think I found what you mean. I attached the filtered mail.log https://justpaste.it/369gu <-there

Is this really often enough to upset pam? Does dovecot use pam or something else?

Depends on your fail2ban settings, but it probably is.
Check also /var/log/fail2ban.log (or similar).
But most importantly fix the issue with this particular user :slight_smile:

And there fail2ban is, banning the office, like 10k times. Now I just gotta track down the user. @toreskev Can I buy ya a cup of Joe friend?

The user is mentioned in the log snippet you posted, anewhope

I’m more of the beer type, but a good brew is fine :wink:

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