SSL Email?

Just want to confirm but since my site is https:// internal messages that are sent from member to member are encrypted are they not?  What would be the difference between a message sent between members on https vs http? Is there a difference?  Also is there any reason why attachments are not part of the internal messaging system?  

Has anyone designed a module to add that capability? 

The internal message system only stores the messages in the database, this has nothing to do with SSL between your PC and the server. Do you want the messages to be encrypted in the database or do you speak about outgoing copies of these messages to the users?

Really any part of the journey that would include the start and end of the message... 

Remember that the internal email message system is not really email.  Attachments should be possible; it would be handled through Dolphin's file system and stored on the server.  How to make it so that only the person you want to receive the email can download the file is the more interesting part of having attachments to the internal message system.