IMAP STARTTLS doesn't work after upgrade from 10.2 to 10.4.4

[cmatias]

Hi.
I'm running 2 identical servers under CentOS / Plesk .
Today I upgraded both servers from 10.2 to 10.4.4.
I usually connect to IMAP courrier server on both machines with STARTTLS security and PASSWORD authentication., but after that upgrade, one of the two servers doesn't works no more with STARTTLS on sending emails.

Email clients report "enable to establish secure connection ..."
I looked on the logs , but found nothing interesting.

Any help will be much appreciated, because this server is hosting 28 domains, and I'm sure all my customers will call me about it tomorrow morning (monday).

Best regards.
Carlos