This article details how to disable SSL\TLS in Apple Mail.
If your email client is configured to connect using SSL\TLS, this may cause PGP Desktop to function incorrectly. This is a condition that is incompatible with PGP Desktop proxying your email. To resolve this, disable the SSL|TLS connection in your mail client.
If the Warn if email client attempts SSL/TLS option is enabled, PGP Desktop displays a warning dialog if the email client attempts SSL/TLS (This option is selected by default.)
|Note: This option should be enabled only if you are certain your mail server supports SSL. It ensures that PGP Desktop will not fall back to sending or receiving messages with the mail server over an unprotected connection if, for example, a problem occurs while negotiating SSL protection for the connection. If you enable this option and your mail server does not support SSL, PGP Desktop will not send or receive any of your messages.|
PGP will do its best to provide SSL/TLS protection. It first tries the alternate port, then it attempts STARTTLS (if supported by the server), finally, if the above fails, it connects to the server unprotected.
To disable SSL\TLS
Restart Apple Mail.