Email "Failed Delivery" message

When you get mail from a "MAILER-DAEMON" or a "Mail Delivery Subsystem" with a subject similar to "Failed Delivery," this means that a message you sent was undeliverable and has been bounced back to you. These messages are produced automatically and usually include a reason for the delivery failure.

Failed or "bounced" messages normally consist of two parts:

  1. The reason for the bounce
  2. Your original message.

Example failure notice

Hi. This is the qmail-send program at yahoo.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

123.45.67.89 failed after I sent the message.
Remote host said: 554 delivery error: dd This user doesn't have a yahoo.com account (testing123@yahoo.com) [-5] - mta123.mail.mud.yahoo.com

--- Below this line is a copy of the message.

Return-Path:
Received: (qmail 24519 invoked by uid 60001); 11 Nov 2010 15:37:25 -0000
...
...
X-Mailer: YahooMail/11.4.9 YahooMailWebService/0.8.107.285259
Date: Thu, 11 Nov 2010 07:37:24 -0800 (PST)
From: Yahoo Customer Care
Subject: Test Message
To: testing123@yahoo.com
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="0-162906830-1289489844=:24510"

--0-162906830-1289489844=:24510
Content-Type: text/plain; charset=us-ascii

[Text of the original message here]

--0-162906830-1289489844=:24510--

The most common reason for a failed delivery is that the email address you entered isn't valid. If the Mailer Daemon says that the account doesn't exist, double-check the spelling of the address you entered. A single misplaced letter can be enough to cause a failed delivery. If the message continues to be bounced back to you, you might want to verify that the account hasn't been closed or moved.