I have no experience with Outlook, but I have a Microsoft-hosted e-mail address that is also accessible via the standard IMAP protocol. If that's your case as well, then mel-base will get your started with mail processing in Common Lisp.
For most stuff that matters, I don't use IMAP directly because I often work off-line. I use isync to synchronize folders on my account with local Maildir folders, and then I work on those folders using mel-base.