RFC822 (and several subsequent RFCs) defines the structure of an
email message in the Internet. It has become the generic standard
for email messages.
It defines a message format containing two parts:
A set of headers, some of which are are
mandatory and others optional. The headers have a fixed format,
consisting of a keyword which starts immediately after a newline,
followed by a colon character, followed by a space and a value.
Some headers include:
From: pscott@ironbark.bendigo.latrobe.edu.au
To: hjc@ironbark
Reply-To: p.scott@latrobe.edu.au
Subject: Problems in Indy lab?
A body, which may contain any plain ASCII
text. The body part follows the headers, separated from them by a
blank line. There are certain rules which ensure that no line in
the body can be mistaken for a header line, even though the two
parts are logically distinct. Note that more recent standards than
RFC822 (MIME) extend the range of possible
messages which can be sent by email as enclosures
or attachments, see later.