Title: Bounce message
Content: MUST construct an "undeliverable mail" notification message and send it to the originator of the undeliverable mail (as indicated by the reverse-path)."" This rule is essential for SMTP: as the name says, it's a 'simple' protocol, it cannot reliably work if mail silently vanishes in black holes, so bounces are required to spot and fix problems. Today, however, it can be common to receive mostly spam emails, which usually uses forged Return-Paths. It is then often impossible for the MTA to inform the originator, and sending a bounce to the forged Return-Path would hit an innocent third party. In addition,

Title: Variable envelope return path
Content: message with the undeliverable address that caused the bounce. If the mailing list software can see that a bounce resulted from an attempt to send a message to user@example.com then it doesn't need to understand the rest of the information in the bounce. It can simply count how many messages were recently sent to user@example.com, and how many bounces resulted, and if the proportion of bounced messages is too high, the address is removed from the list. While bounce message formats in general vary wildly, there is one aspect of a bounce message that is highly predictable: "the address to

Title: Bounce message
Content: numerical 3-digit value, the SMTP response contains itself a human readable part. The information Bounce message A bounce message or just "bounce" is an automated message from a mail system, informing the sender of a previous message that that message had not been delivered (or some other delivery problem occurred). The original message is said to have "bounced". More formal terms for bounce message include "Non-Delivery Report" or "Non-Delivery Receipt" (NDR), [Failed] "Delivery Status Notification" (DSN) message, or a "Non-Delivery Notification" (NDN). Errors may occur at multiple places in mail delivery. A sender may sometimes receive a bounce message from

Title: Bounce message
Content: sense, bounces sent with a non-empty Return-Path are incorrect. RFC 3834 offers some heuristics to identify incorrect bounces based on the local part (left hand side before the "@") of the address in a non-empty Return-Path, and it even defines a mail header field, Auto-Submitted, to identify auto replies. But the mail header is a part of the mail data (SMTP command DATA), and MTAs typically don't look "into" the mail. They deal with the "envelope", that includes the MAIL FROM address (a.k.a. Return-Path, Envelope-FROM, or "reverse path") but not, e.g., the RFC 2822-From in the mail header field From.

Title: Variable envelope return path
Content: not enough room left to accept any more. When a message is sent to a mailing list, the mailing list software re-sends it to all of the addresses on the list. The presence of invalid addresses in the list results in bounce messages being sent to the owner of the list. If the mailing list is small, the owner can read the bounce messages and manually remove the invalid addresses from the list. With a larger mailing list, this is a tedious, unpleasant job, so it is desirable to automate the process. Unfortunately, most bounce messages have historically been designed

Question: Where does a bounced email return to?
Answer: Sender