After trying to upgrade our (very) old Tine 2.0 installation to the latest version of Tine 2.0, Tine 2.0 was not able to connect to our mailservers any more. After testing a few things, it became clear that the PHP IMAP module had problems with the SSL certificate we are using for our mailservers. Even though it is not a self-signed certificate, imap_open() failed to connect to the mailserver. After digging a bit in the Tine 2.0 sources, I found that peer verification can be disabled by setting the peerVerify flag to false. Since I could not find a UI setting in the Tine 2.0 setup for this option, the solution was simple: Look for the imap configuration in the tine20_config database table and add the peerVerify:false setting to the existing JSON object for the connection configuration.