rfc2822 April 2001

3.6.6. Resent fields

   Resent fields SHOULD be added to any message that is reintroduced by
   a user into the transport system.  A separate set of resent fields
   SHOULD be added each time this is done.  All of the resent fields
   corresponding to a particular resending of the message SHOULD be
   together.  Each new set of resent fields is prepended to the message;
   that is, the most recent set of resent fields appear earlier in the
   message.  No other fields in the message are changed when resent
   fields are added.

   Each of the resent fields corresponds to a particular field elsewhere
   in the syntax.  For instance, the "Resent-Date:" field corresponds to
   the "Date:" field and the "Resent-To:" field corresponds to the "To:"
   field.  In each case, the syntax for the field body is identical to
   the syntax given previously for the corresponding field.

   When resent fields are used, the "Resent-From:" and "Resent-Date:"
   fields MUST be sent.  The "Resent-Message-ID:" field SHOULD be sent.
   "Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be
   identical to "Resent-From:".
resent-date     =       "Resent-Date:" date-time CRLF

resent-from     =       "Resent-From:" mailbox-list CRLF

resent-sender   =       "Resent-Sender:" mailbox CRLF

resent-to       =       "Resent-To:" address-list CRLF

resent-cc       =       "Resent-Cc:" address-list CRLF

resent-bcc      =       "Resent-Bcc:" (address-list / [CFWS]) CRLF

resent-msg-id   =       "Resent-Message-ID:" msg-id CRLF

   Resent fields are used to identify a message as having been
   reintroduced into the transport system by a user.  The purpose of
   using resent fields is to have the message appear to the final
   recipient as if it were sent directly by the original sender, with
   all of the original fields remaining the same.  Each set of resent
   fields correspond to a particular resending event.  That is, if a
   message is resent multiple times, each set of resent fields gives
   identifying information for each individual time.  Resent fields are
   strictly informational.  They MUST NOT be used in the normal
   processing of replies or other such automatic actions on messages.

   Note: Reintroducing a message into the transport system and using
   resent fields is a different operation from "forwarding".
   "Forwarding" has two meanings: One sense of forwarding is that a mail
   reading program can be told by a user to forward a copy of a message
   to another person, making the forwarded message the body of the new
   message.  A forwarded message in this sense does not appear to have
   come from the original sender, but is an entirely new message from
   the forwarder of the message.  On the other hand, forwarding is also
   used to mean when a mail transport program gets a message and
   forwards it on to a different destination for final delivery.  Resent
   header fields are not intended for use with either type of
   forwarding.

   The resent originator fields indicate the mailbox of the person(s) or
   system(s) that resent the message.  As with the regular originator
   fields, there are two forms: a simple "Resent-From:" form which
   contains the mailbox of the individual doing the resending, and the
   more complex form, when one individual (identified in the
   "Resent-Sender:" field) resends a message on behalf of one or more
   others (identified in the "Resent-From:" field).

   Note: When replying to a resent message, replies behave just as they
   would with any other message, using the original "From:",
   "Reply-To:", "Message-ID:", and other fields.  The resent fields are
   only informational and MUST NOT be used in the normal processing of
   replies.

   The "Resent-Date:" indicates the date and time at which the resent
   message is dispatched by the resender of the message.  Like the
   "Date:" field, it is not the date and time that the message was
   actually transported.

   The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function
   identically to the "To:", "Cc:", and "Bcc:" fields respectively,
   except that they indicate the recipients of the resent message, not
   the recipients of the original message.

   The "Resent-Message-ID:" field provides a unique identifier for the
   resent message.