rfc2822 April 2001

1.1. Scope

   This standard specifies a syntax for text messages that are sent
   between computer users, within the framework of "electronic mail"
   messages.  This standard supersedes the one specified in Request For
   Comments (RFC) 822, "Standard for the Format of ARPA Internet Text
   Messages" [RFC822], updating it to reflect current practice and
   incorporating incremental changes that were specified in other RFCs
   [STD3].

   This standard specifies a syntax only for text messages.  In
   particular, it makes no provision for the transmission of images,
   audio, or other sorts of structured data in electronic mail messages.
   There are several extensions published, such as the MIME document
   series [RFC2045, RFC2046, RFC2049], which describe mechanisms for the
   transmission of such data through electronic mail, either by
   extending the syntax provided here or by structuring such messages to
   conform to this syntax.  Those mechanisms are outside of the scope of
   this standard.

   In the context of electronic mail, messages are viewed as having an
   envelope and contents.  The envelope contains whatever information is
   needed to accomplish transmission and delivery.  (See [RFC2821] for a
   discussion of the envelope.)  The contents comprise the object to be
   delivered to the recipient.  This standard applies only to the format
   and some of the semantics of message contents.  It contains no
   specification of the information in the envelope.

   However, some message systems may use information from the contents
   to create the envelope.  It is intended that this standard facilitate
   the acquisition of such information by programs.

   This specification is intended as a definition of what message
   content format is to be passed between systems.  Though some message
   systems locally store messages in this format (which eliminates the
   need for translation between formats) and others use formats that
   differ from the one specified in this standard, local storage is
   outside of the scope of this standard.
   Note: This standard is not intended to dictate the internal formats
   used by sites, the specific message system features that they are
   expected to support, or any of the characteristics of user interface
   programs that create or read messages.  In addition, this standard
   does not specify an encoding of the characters for either transport
   or storage; that is, it does not specify the number of bits used or
   how those bits are specifically transferred over the wire or stored
   on disk.