• TT65

      Moolevel 0
    • Post #1

    Hi everyone,
    for the first time I’m playing around with mailcow and I like it. On my current default setup (2025-03b) I stumbled across a strange behaviour and wanted to know if this is normal or not (and how to fix it).

    I setup an (catch-all) alias for a domain. If I send an email from an external provider to this alias domain everything seems fine in thunderbird until I click on “Reply” or “Reply to all”. The “From” and “To” addresses won’t flip like:

    “From” becomes "To and “To” becomes “From”.

    If I send a mail to the default mailbox email address everything is as it should be. Has anyone noticed this behavior or perhaps been able to recreate it - maybe a fix for it?

    • DaRon

        Moolevel 1
      • Post #2

      Can you check the header of the received mail?
      check the “From:” if this is the correct sender and the “To:” if its the correct receiver? or if its even filled at all and how?

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      • TT65

          Moolevel 0
        • Post #3

        In the header there are the following elements:

        • Delivered-To: “mail@mailbox_domain.tld”
        • Received: from mailcow mailserver … for “mail@mailbox_domain.tld”
        • X-Original-To: “alias@mailbox_domain.tld”
        • Received: from external mailserver … for “alias@mailbox_domain.tld”
        • From mail@external_email_provider.tld"
        • To: “alias@mailbox_domain.tld”

        So far everything looks normal to me.
        I also compared the source code of the two emails and one thing I noticed so far was that the “alias” mail was received via IPv6 and the “default mailbox” mail via IPv4. For the other things I have to clean up the source a little bit.

        For a quick cross check I setup another server which has the same strange behaviour.

        • TT65

            Moolevel 0
          • Post #4

          After some long debug sessions Thunderbird is the reason why it ends up so strange. If I add an identity for this alias then the email or lets the logic gets setup correctly.

          I was not expecting Thunderbird as the party crasher the first time because I have been using “aliases” with another provider for a long time and Thunderbird has never had any problems there - instead of the “alias”, the standard email domain was used.

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