Undelivered Mail Returned to Sender

I sent email, but it was returned to me. What should I do?
Check the email address to which you attempted to send the email.

A typo (typing mistake) in the email address is the most common reason for the return of email that you sent, so generally, the first place to look is at the email address itself.

If the email is typed correctly, contact the administrator of the server from where the returned email came. Supply a copy of the error message appended to the returned the mail: please do not send the personal part of the email.

These are the main reasons for a correctly typed email address not being delivered:

  • Unable to find the host mail server.
  • Found the host mail server, but unable to find the user's account.
  • Unable to deliver at all.

These reasons and causes are dealt with in more detail below.

Refrain from sending repeated emails to the same email address (hoping that one of your attempts will work) until you have been able to understand the reason for your email not being delivered.


Reasons for returned email

When your email is returned undelivered, you will find an error message appended to it.
The Postfix progam part of the error message supplies a clue for the reason for your email being returned.

An example of a returned email's error message

In this example, the mail has been returned "User unknown".

-------------------------------------------------------------
This is the Postfix program at host mx1.asahi-net.or.jp.

I'm sorry to have to inform you that the message returned
below could not be delivered to one or more destinations.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the message returned below.

The Postfix program

<tech@desk.asahi-net.or.jp@mx1.asahi-net.or.jp>: User unknown:
"tech@desk.asahi-net.or.jp"
-------------------------------------------------------------

  • User unknown
    • Your email reached the host mail server, but that server couldn't locate the user owning the email address you wrote to. Commonly this is caused by a mis-type of the user part of the email address (the part before the "@"). Please check the email address again.

      Another cause of the User unknown message is that you have replied to somebody's email, but that person has mis-typed their email address in the "Reply address" section of their email program. Therefore when you attempt to reply to their email by clicking the Reply button in your email program, you are replying to the wrong address.
  • Host unknown
    • Your email did not reach the host mail server. Commonly this is caused by a mis-type of the domain name part of the email address (the part after the "@"). Please check the email address again.

      Another cause of the Host unknown message is that the host mail server itself is experiencing technical problems, or there are problems on the network on which the host mail server is located.
  • The user(s) account is temporarily over quota / Message size exceeds fixed maximum message size / Exceeded storage allocation
    • Your email reached the host mail server, and the server located the user owning the email address you wrote to and tried to put your email into their mailbox. But the user's mailbox was either full or your email was too big to fit into the mailbox. Either way, your email was returned to you undelivered.

      You could try to send a reduced (in size) version of your email to see if it is delivered. That way you may be able to warn the user that you are having prolems sending your email.
  • Cannot send message for (n) days (n) weeks unable to deliver mail
    • Your email reached the host mail server, but the server couldn't or wouldn't accept it. The sending mail server tried to send your mail again, but it was rejected again. This process continued for several days or weeks, and then gave up. Your email was returned to you undelivered.

      A cause of this could be the host mail server itself experiencing technical problems. Or the host server may have been configured (on purpose or accidentally) to reject your email.
  • Local configuration error
    • This is a message from the sending server. The most common cause of this is an error in the settings of your email software. Please check your email software's settings.