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Sudowned
Asked: 2014-03-16 08:56:08 +0800 CST

What does Courier do with undeliverable messages?

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On Wednesday we had an unrelated email issue with our host, and they made some changes which included removing our domain, foo.com, from /etc/local_domains.

This had some far-reaching (and difficult to diagnose) implications, and we didn't actually notice that mails weren't being delivered at all until Thursday. I spent Thursday mistakenly trying to figure out what was wrong with our email cronjobs, but on Friday I finally found the real problem and fixed it.

The issue now is that there's a lot of email missing from the last two days. I need to find those missing messages if at all possible, but unfortunately googling for "courier where do failed emails go" results in a bunch of news stories about meatspace shipments. I've checked inside /var/mail but the files within are empty - I guess cPanel or Courier does things I don't expect with email.

My question is: Where would the undeliverable mails from that period go? Is there any possibility they still exist somewhere and I can recover them?

courier

1 Answers

  1. Best Answer

    The cpanel /etc/local_domains is probably used to configure exim, not courier. Incoming emails are delivered via smtp, not pop nor imap.

    So here is what happened:

    • Remote mail servers looked for a MX server for your domain
    • Your dns configuration is probably set up so that your cpanel server is the MX server with the best priority for your domain
    • The remote mail servers connected to exim on your server. Since your domain was not configured on exim, exim interpreted the connexion as a RELAY request, and very likely told the remote mail servers to get stuffed.

    So the emails are not on your server, sorry.

    Then there is a very little hope: If Exim rejected the incoming emails with 5xx error message, there are few chances the remote servers kept the message. But if Exim rejected the incoming emails with a 4xx error message, then 2 things could happen:

    1. You have configured several MX servers for your domain. Go have a look on the other mail servers if by any chance they received the emails and stored them for future delivery.
    2. The 4xx error message is supposed to be "temporary", so this means that the remote mail servers will keep the message in queue and try it again for a certain amount of time, depending on their configuration. Maybe you are currently receiving "old" emails which were rejected when you had the wrong configuration in place.

    So, in order to find if other MX servers are configured for your domain:

    dig foo.com mx

    Then in order to check the answer of your SMTP server to relay requests:

    • on a remote client ( the important point is to have an external ip address ):

    telnet your-server-ip-address 25

    HELO helo.com

    MAIL FROM: <[email protected]>

    RCPT TO: <[email protected]>

    After each line ( HELO, MAIL FROM, RCPT TO ) you will have an answer from your server. The answer to the RCPT TO: should be 5xx .. or 4xx .. . If it is 4xx you have a little hope.

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