What is a bounced email ?

A bounced email ( simply a bounce ) is a email message from mail server (MTA) informing the sender of another message about a delivery error.

It is also called as a returned mail, an error email, and an undelivered mail. More information about bounced email is described in en.wikipedia.org/wiki/Bounced_e-mail .


The first appearance: bouncehammer.jp/en/what-is-bounced-email

Features of Bounced Email

A bounced email have the following features.

Subject Header

A bounced email is created by MTA ( Such as Sendmail, Postfix, and qmail ) automatically when delivery error occurred. Contents of the subject header of bounced email like followings.

  • Returned mail: see transcript for details
  • Mail System Error - Returned Mail
  • Non Delivery Notification
  • DELIVERY FAILURE: ...
  • Undelivered Mail Returned to Sender
  • Postmaster notify: see transcript for details
  • Delivery Status Notification (Failure)
  • Warning: could not send message for past 4 hour
  • failure notice

From Header

A sender of bounced email is mainly a postmaster or a MAILER-DAEMON. You will find names like the followings in From: header of bounced email.

  • MAILER-DAEMON
  • MAILER-DAEMON@HOSTNAME OF SENDER'S MAIL SERVER
  • MAILER-DAEMON@HOSTNAME OF RECIPIENT'S MAIL SERVER
  • Postmaster
  • Postmaster@HOSTNAME OF SENDER'S MAIL SERVER
  • Postmaster@HOSTNAME OF RECIPIENT'S MAIL SERVER
  • Mail Delivery Subsystem
  • Mail Delivery System
  • Mail Administrator

Message Body

A bounced email is created by mail server program such Sendmail, and contains delivery report in its message body. Sisimai reads a bounced email and parse its headers and its message body, then find details about why the delivery failed. The following section is particularly important to find details for Sisimai.

  • Status: 5.1.1 <- Various error codes
  • Diagnostic-Code: ... <- Error message, response of SMTP server, and so on.

Sisimai is a library which parses a bounced email, finds a reason of bounce.