How to accept (and remove) TLS/SSL certificates for eMail in MacMail ?

When I try to access my email server then I want to receive/send these emails through

a) TLS
or
b) SSL

Is MacMail v3.5 able to use TLS? If yes: Where do I have to enable TLS?

When I use SSL then I should be prompted by the email server to accept the server certificate. However I am NOT prompted currently.
Either because I have unintentionally accepted it previously or I suppress the prompt somehow or I use an old certifcate.

Receiving is no problem but sending.
Server logs show some timeouts in send sessions.

How can I solve the problem?

Where can I find the currently stored certifcates for MacMail v3.5?
How can I delete them?

How can I revert back to an unencrypted send? Read: How do I turn off TLS resp. SSL completely?

Peter