Electronic mail protocols are application layer protocols.
Mail servers use SMTP to send and receive mail messages. User-level client mail applications use SMTP for sending messages to a mail server for relaying and use another protocol to receive messages: POP, IMAP or a proprietary system such as Microsoft Exchange or Lotus Notes/Domino.
Electronic mail protocols are often combined with cryptographic protocols. Information related to such protocols (IMAPS, STARTTLS etc.) should also be submitted to this category.
This is a collection of links to pages which explain various protocols related to email handling. If you are looking for mail software, go look in Computers:Software. This is for people interested in understanding how the mail system itself works.
Please provide HTTP links to the canonical location at http://www.rfc-editor.org/. Informational and historic RFCs should only be added if of special interest.