Free IMAP Resources
Email Protocols : SMTP, MIME, POP and IMAP
These are presentation slides including information about smtp, and the other email protocols
Eudora Email Primer (pdf link)
"Section Two, POP, IMAP, and Real World Issues, discusses the two most popular mail access protocols today, POP and IMAP, and how they implement mail access modes to provide real-world solutions for today?s formidable email challenges."