RFC822 defines the structure of an email message in the Internet.
It has become the generic standard for all email messages. RFC2822
updates RFC822 without substantially changing its approach.
An RFC822-compatible email message consists of lines of ASCII
text. It contains two sections:
An email message begins with a set of headers
(or header lines), 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 (ie, left-justified),
followed by a colon character, followed by a space and a value --
sometimes called "name-value pairs". Some typical headers include:
From: pscott@ironbark.bendigo.latrobe.edu.au
To: hjc@redgum.bendigo.latrobe.edu.au
Reply-To: p.scott@latrobe.edu.au
Subject: Problems with redgum?
A body, which may contain any plain
ASCII text. The body part follows the headers, separated
from them by a blank line. 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.