SMTP STARTTLS problem occurs once in a while

[e-d-i-t]

I had this problem before and eventually rebooted the server but that did not fix it.
After a restart of the Zimbra serivces (zmcontrol restart, cause a reboot does not work for some reason...) my eMClient mail client was able to send mail again.

And today, I guess a month later, it appeared again. a dialog with SMTP STARTTLS error from the mailclient.
So now I restarted Zimbra services and it works again.

I have a valid COMODO certificate installed, but I have no clue what to look for.
IMAP connections seem to work, but sending SMTP fails on that moment. (Might be the client itself? Have to test that using webmail I guess when it occurs again)

[e-d-i-t]

Ah, and just now delayed mail from early this morning comes in. My batchedSMTP delived it.
So SMTP has been giving problems for over 12 hours now. As I am migrating, I haven't got that much traffic jet but it will be busy once fully migrated.

That is, until I know what is bugging the system...

[phoenix]

What do you see in the log files?

[e-d-i-t]

I am prety a noob in Zimbra, so I need to figure out which logfile to look into.
Also a Windows-guy quite a bit so I want to open those logs with WinSCP, but don't know the zimbra user password.
Not quite sure if I can just reset that password and not killing the server.

[e-d-i-t]

I was able to view some logging, but I cannot find any logs about SMTP-connections.
Is that found elsewhere on the server? Or should that be somewhere in /opt/zimbra/log ?