Bounce address

All of these names refer to the email address provided with the MAIL FROM command during the SMTP session.

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 paper letter in an envelope, then the "header fields", such as To:, 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.

These typically take advantage of properties of the bounce address, such as: Extended uses include mailing list handling in Variable envelope return path (VERP), email authentication via SPF, spam filtering, and backscatter reduction in Bounce Address Tag Validation.