I have ZCS 8.8 on Ubuntu 16.04, serving some 3000 email accounts.
Mostly there's no problem and everything is working fine...
...except rare, but very disturbing annoyances, which I do not have idea how to approach:
- Sometimes descriptions vanish from calendar event. All remember they were there, but next day...gone. Just calendar event with TITLE, but BODY is empty.
- Sometimes mail attachments vanish. User remembers there were, for example, 3 attachments, and indeed sender says 3 were sent, but now only 1 is attached to mail.
- Maybe not related...Outlook IMAP sync works just fine for 1 week, then it begins striking for a day or two (user needs to either click Send/Receive button, or click to other mail account then back to refresh Inbox in Outlook). After few days all works fine again, without restarting Outlook or server.
Those issues are VERY RARE, but still they occure more and more often. It was once a year before, but lately it is once or twice per month to receive one such complaint.
What I might have suspected it network/server load or even TLS connection breaking, but I do not have enough evidence on this. Server is generally not overloaded, usually creeping between 5 and 10% CPU load.
Any idea what to check, look for, debug?