We most certainly are checking cert validity. It is possible your cert is self-signed, or from a non trusted CA, or expired.
We also check for secure cipher suites and either fail or prompt the user to accept an insecure connection. We recently deprecated RC4 which caused quite a few support tickets. That could causing your connections to fail.
It sounds like you just got a confusing response from a CS agent (it is a complicated topic). They might be mixing up instructions for IMAP and Exchange which typically runs on 443.
Contact support again and ask them to assign it to Mike from Engineering and I will look into your problem.
We also check for secure cipher suites and either fail or prompt the user to accept an insecure connection. We recently deprecated RC4 which caused quite a few support tickets. That could causing your connections to fail.
It sounds like you just got a confusing response from a CS agent (it is a complicated topic). They might be mixing up instructions for IMAP and Exchange which typically runs on 443.
Contact support again and ask them to assign it to Mike from Engineering and I will look into your problem.