Responsibilities and envelopes
Moving a message closer to a remote recipient
MXPS: the Mail Exchanger Protocol Switch
CNAME records in mail
IP addresses in mail
Programs that read mail divide each message into a header and a body. There are separate pages describing the header format.
Usually the body of a message is human-readable text. However, users often ``attach'' files in other formats. For example, uuencode is a simple method of safely encoding any binary file as lines of text inside a message. The most popular structure for attachments is MIME, which includes a file-format naming scheme. MIME is not discussed here.
Once a message is delivered to a user's mailbox on a central server, the user can log in to the server and retrieve the message. The most popular protocol dedicated to this task is POP. Another protocol, offering many more mailbox-processing features, is IMAP. POP and IMAP are not discussed here.