What is a Bounce Email and how it works?

About

When an email is rejected by an smtp email server, an email is returned that is called a bounce email.

What is the bounce procedure?

When an SMTP server can't deliver a message to a mailbox, a bounce message is returned to the original sender.

The bounce message is returned with:

• an empty sender
• the recipient as the original sender
• a message body: We were unable to deliver the following message xxx

How to identify the bounce address?

With the bounce message

The bounce message may not:

• identify the address that failed.
• include a copy of the original message.
• and more RFC 1211 - Problems with the maintenance of large mailing lists

With Variable envelope return path (VERP)

The Variable envelope return path (VERP) ¹⁾ is a technique that helps to identify the bounce email address.

A VERP is a envelope where the sender address has the original author in its tag.

Example of sender email address where the sender is [email protected] and the tag is bob=example.org

[email protected]

With DSN (Delivery Status Notification)

This problem could be solved with the DSN option (see Rfc 1891, Rfc 1892, and Rfc 1894) Unfortunately, the DSN option is useless because it's mostly not supported the MTA.

With the X-Failed-Recipients

Some SMTP provider adds the header X-Failed-Recipients that indicates the failed recipients.

X-Failed-Recipients: [email protected]