Outlook 2016 and ZCS 8.6.0

[MartinsBonders]

We have strange problem. We have Outlook 2016 configured with IMAP, when you open Outlook, everything is working fine, but after some 4-6 hours something is going wrong. Send and Receiving stop on 50% and no errors. Just status bar show send and receiving 50% and that all, this message can stay a couple of hours and no error. Just synchronizing folders. Then you close Outlook and open, after Outlook gets all the last hour messages. What could be the problem? It looks like Outlook hang on some session on something like that.

[MartinsBonders]

After some time Outlook give me error: ERROR: "Your server unexpectedly terminated the connection. Possible causes include server problems, network problems, or a long period of inactivity.", hr=2148322319
This is error from IMAP log file from Outlook debug mode.
Is there some Zimbra IMAP session lifetime or timeout settings?

[MartinsBonders]

Now we have ZCS 8.7.7 and the same issue. After some 5-6 hours, Outlook 2016 no more getting e-mails. Outlook must be reopened. It there some guesses what could be the problem?