Client-Server Mail Protocols FAQ
   A brief summary of POP3, SMTP, and IMAP, including pointers to sources and frequently-asked-questions sites.
   http://www.faqs.org/faqs/mail/mailclient-faq/

Email Addressing FAQ
   The user+box@host addressing FAQ. A discussion of what exactly is permissible and verifiable in an e-mail address.
   http://faqs.org/faqs/mail/addressing/

Internet Mail Consortium
   Information about IMC and its members, all the Internet mail standards, and links to several IMC-hosted mailing lists.
   http://www.imc.org/

MIME Meta-FAQ
   comp.mail.mime meta-FAQ: Help for MIME problems. Pointers to information about Multipurpose Internet Mail Extensions and some answers to common problems with MIME.
   http://www.faqs.org/faqs/mail/mime-faq/mime0/

Message Access Paradigms and Protocols
   Provides extensive background and compares the Post Office Protocol (POP) with the Internet Message Access Protocol (IMAP).
   ftp://ftp.cac.washington.edu/mail/imap.vs.pop

The IMAP Connection
   University of Washington collection of IMAP documentation and resources.
   http://www.imap.org