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

Internet Mail Consortium
Information about IMC and its members, all the Internet mail standards, and links to several IMC-hosted mailing lists.

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.

The IMAP Connection
University of Washington collection of IMAP documentation and resources.