MAIL FROM
command during the Background information
Ordinarily, the bounce address is not seen by email users and, without standardization of the name, it may cause confusion. If an email message is thought of as resembling a traditional paperTo:
, From:
, and Subject:
, along with the body of the message are analogous to the letterhead and body of a letter - and are normally all presented and visible to the user. However, the envelope in this analogy is the contents of the MAIL FROM
and RCPT TO
fields from the SMTP session - and neither of these is normally visible to the user.
While it is most common for the To:
and From:
information in the letter to be the same as the "envelope" values, such is not always the case. For example, on RCPT TO
command to determine where the email should go, and the MAIL FROM
command to indicate where it came from.
Usage
While its original usage was to provide information about how to return bounce messages, since the late 1990s, other uses have come about. These typically take advantage of properties of the bounce address, such as: *It is given early in theFrom:
, Sender:
, Resent-from:
, etc.) or be missing entirely.
Extended uses include mailing list handling in Terminology
The various terms have different origins and sometimes different meanings, although these differences have often become moot on the modern internet. * bounce address - When an email can not be delivered, the MTA will create aMAIL FROM
command. Used in RFC 4406.
* return path - When the email is put in the recipient's MAIL FROM
command. Earlier forms of email (such as MAIL FROM
command, whose content is supposed to consist of the envelope sender address. Used in RFC 5321, RFC 3464, RFC 3834, Internet Mail Architecture.
* envelope from - information that the SMTP protocol uses analogous to the envelope of a letter. Used in RFC 5230, RFC 5233.
* envelope sender address - the mailbox address in a non-empty reverse path excluding any (deprecated) reverse routing info. Used in RFC 2821, RFC 3461, RFC 3464, RFC 3798, RFC 5228.
* envelope return address - similar to envelope sender address, used in RFC 3461, RFC 3464, RFC 3834, RFC 4952.
* MAIL FROM - This variation comes directly from the SMTP MAIL FROM
command name. Used in RFC 5321, RFC 3464, RFC 3834, RFC 4408, RFC 4409, RFC 4952.
* 2821-FROM - Until October, 2008, SMTP was defined in RFC 2821, while the body of the email was defined in RFC 2822. The term "2821-FROM" makes it clear that the address referred to is the MAIL FROM
information, while "2822-From:" refers to the address in the "From:" header seen by end users. Used in RFC 5598.
* 5321-FROM - Evolution of 2821-FROM as from October, 2008, SMTP has been defined in RFC 5321.
* return address - Another term that comes from the letter analogy for email. used in RFC 5321, RFC 3834.
* From_ - When an email gets delivered to the user's MAIL FROM
command was placed on a line beginning with "From" followed by a single space, the "From_" term uses an underscore to represent the space to distinguish it from the "From:" mail header. In this mailbox format, lines in the actual email that begin with a "From " have to be escaped and changed into lines that begin with ">From ".
See also
*