Clonsigna is very easy to use and follows the rfc3501 and rfc5256
specifications.
It allows both IMAP and IMAP over SSL communications.
The most of the commands output has it's own message parser that maps a server reply to a Common Lisp
element (usually plists and classes).
Mail messages are completely handled and decoded by clonsigna parsers so that you'll have a
mail message "ready to use".