I installed a monitoring tool so I am alerted in case the box goes down for whatever reason. Seems that every night “https://box.domain.net/mail” is unavailable for about a minute around 4am CET. I also monitor “ns1.box.domain.net” which does not display the same issue.
Is there some maintenance running daily that could explain this or should I just ignore this?
MIAB will stop accepting mail whilst it performs a backup. This is scheduled to run at some point in the 03:00 hour per the time/timezone of the server [mine runs at 03:35]. I imagine this is what you are seeing.
Glad to be of help. Of course, any properly configured mail server will re-attempt delivery of mail if MIAB happens to be unavailable when it tries so this should not result in any lost mail.