Bounce address
Encyclopedia
A bounce address is an e-mail address
to which bounce message
s are delivered. There are many variants of the name, none of them used universally, including return path, reverse path, envelope from, envelope sender, MAIL FROM, 5321-FROM, return address, From_, Errors-to, etc. It is not uncommon for a single document to use several of these names.
All of these names refer to the e-mail address found by the SMTP
MAIL FROM command.
While it is most common for the To and From information in the letter to be the same as on the envelope, such is not always the case. For example, on electronic mailing list
s, the information seen in the "From:" header will come from the person who sent the e-mail to the list, while the bounce address will be set to that of the mailing list software, so problems delivering the mailing list messages can be handled correctly.
When e-mail is transported using the Simple Mail Transfer Protocol
(SMTP), the most common method on the internet, only the envelope information is looked at to figure out where the e-mail should go; the body of the e-mail is not examined. Mail Transfer Agent
s (MTA) using the SMTP protocol use the RCPT TO command to determine where the e-mail should go, and the MAIL FROM command to indicate where it came from.
Extended uses include mailing list handling in Variable envelope return path
(VERP), e-mail authentication
, spam filtering, and backscatter
reduction in Bounce Address Tag Validation
.
E-mail address
An email address identifies an email box to which email messages are delivered. An example format of an email address is lewis@example.net which is read as lewis at example dot net...
to which bounce message
Bounce message
In the Internet's standard e-mail protocol SMTP, a bounce message, also called a Non-Delivery Report/Receipt , a Delivery Status Notification message, a Non-Delivery Notification or simply a bounce, is an automated electronic mail message from a mail system informing the sender of another...
s are delivered. There are many variants of the name, none of them used universally, including return path, reverse path, envelope from, envelope sender, MAIL FROM, 5321-FROM, return address, From_, Errors-to, etc. It is not uncommon for a single document to use several of these names.
All of these names refer to the e-mail address found by the SMTP
Simple Mail Transfer Protocol
Simple Mail Transfer Protocol is an Internet standard for electronic mail transmission across Internet Protocol networks. SMTP was first defined by RFC 821 , and last updated by RFC 5321 which includes the extended SMTP additions, and is the protocol in widespread use today...
MAIL FROM command.
Background information
Ordinarily, the bounce address is not seen by e-mail users and, without standardization of the name, it may cause confusion. An e-mail message can be thought of as resembling a letter in an envelope. It will contain "header fields", such as To:, From:, and Subject:, along with the body of the message. These are analogous to the letterhead and body of a letter. The "to" and "from" information is usually copied to the envelope, and used to deliver the message.While it is most common for the To and From information in the letter to be the same as on the envelope, such is not always the case. For example, on electronic mailing list
Electronic mailing list
An electronic mailing list is a special usage of email that allows for widespread distribution of information to many Internet users. It is similar to a traditional mailing list — a list of names and addresses — as might be kept by an organization for sending publications to...
s, the information seen in the "From:" header will come from the person who sent the e-mail to the list, while the bounce address will be set to that of the mailing list software, so problems delivering the mailing list messages can be handled correctly.
When e-mail is transported using the Simple Mail Transfer Protocol
Simple Mail Transfer Protocol
Simple Mail Transfer Protocol is an Internet standard for electronic mail transmission across Internet Protocol networks. SMTP was first defined by RFC 821 , and last updated by RFC 5321 which includes the extended SMTP additions, and is the protocol in widespread use today...
(SMTP), the most common method on the internet, only the envelope information is looked at to figure out where the e-mail should go; the body of the e-mail is not examined. Mail Transfer Agent
Mail transfer agent
Within Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...
s (MTA) using the SMTP protocol use the RCPT TO command to determine where the e-mail 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 the SMTP session, so a message can be rejected without receiving its body.
- It is typically not seen by users so it can be altered to include additional information without confusing them.
- It is a required part of Mail Transfer AgentMail transfer agentWithin Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...
software, so it is easy for other programs to use. In contrast, the "from" address in the body of the mail can be on several different headers (e.g. the From:, Sender:, Resent-from:, etc.) or be missing entirely.
Extended uses include mailing list handling in Variable envelope return path
Variable envelope return path
Variable envelope return path is a technique used by some electronic mailing list software to enable automatic detection and removal of undeliverable e-mail addresses...
(VERP), e-mail authentication
E-mail authentication
Email authentication is the effort to equip messages of the email transport system with enough verifiable information, so that recipients can recognize the nature of each incoming message automatically...
, spam filtering, and backscatter
Backscatter (e-mail)
Backscatter is incorrect automated bounce messages sent by mail servers, typically as a side effect of incoming spam....
reduction in Bounce Address Tag Validation
Bounce Address Tag Validation
In computing, Bounce Address Tag Validation is a method, defined in an Internet Draft, for determining whether the bounce address specified in an E-mail message is valid...
.
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 e-mail can not be delivered, the MTA will create a bounce messageBounce messageIn the Internet's standard e-mail protocol SMTP, a bounce message, also called a Non-Delivery Report/Receipt , a Delivery Status Notification message, a Non-Delivery Notification or simply a bounce, is an automated electronic mail message from a mail system informing the sender of another...
and send it to the address given by the MAIL FROM command. Used in RFC 4406. - return path - When the e-mail is put in the recipient's mailbox, a new mail header is created with the name "Return-Path:" containing the address on the MAIL FROM command. Earlier forms of e-mail (such as UUCPUUCPUUCP is an abbreviation for Unix-to-Unix Copy. The term generally refers to a suite of computer programs and protocols allowing remote execution of commands and transfer of files, email and netnews between computers. Specifically, a command named uucp is one of the programs in the suite; it...
) would require information about each "hop" along the path that the e-mail traveled to reach the destination, hence the "path" part of the name. Used in RFC 2821, RFC 3834, RFC 4409. - reverse path - the argument of the SMTP 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 e-mail 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 latter analogy for e-mail. used in RFC 5321, RFC 3834.
- From_ - When an e-mail gets delivered to the user's mailbox, one file format that may be used is the mboxMboxmbox is a generic term for a family of related file formats used for holding collections of electronic mail messages. All messages in an mbox mailbox are concatenated and stored as plain text in a single file...
format. In this format, the e-mail address from the 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 e-mail that begin with a "From " have to be escaped and changed into lines that begin with ">From ".