in reply to SMTP with SSL
Your talking about two different things here. SSL is the Secure Socket Layer. In the scope of the OSI network model, SSL will encrypt the socket level communications between the sender and the reciever. Thus, both sides would have to be able to use SSL to communicate. Once the message arrives at the other end, the message is stored in a plain text format.
If you want to keep the messages encypted until they are read (which I'm assuming you want to do), you can use a number of encyption methods to generate a garbage message that contains the orginial message. A popular method is PGP, but alternatives include RC5 and Blowfish. As a side note, the reciever will need to have a public key to unlock your message.
CPAN should contain modules for using any of the encryption methods above. Good luck!