I have an exchange server and around 200+ accepted domains (managed service company).

I would like to set up a catch all for postmaster@* I tried doing so via transport rules, but exchange seems to be rejecting the messages "The e-mail address you entered couldn't be found" prior to applying the transport rule

Server: 2008 R2 running Exchange Server 2010 SP3

Test Transport rule:

  • Conditions: When a recipient's address matches postmaster@.+
  • Actions: send rejection message BEACON to sender with enhanced status code 5.7.777 (this would eventually become "redirect the message to address")

Are transport rules the/a correct choice here? Am I correct in guessing that it's checking address validity BEFORE matching a transport rule? Do any of the transport rule conditions get checked before mailbox existence is checked?

Note: I'm open to changing approach if I should be using something other than transport rules

Note: This is not a duplicate of 119649

  • Though I am fluent in powershell and could write a script to create a distribution list that includes them all, I want a solution that's self implementing without having to manually add new domains to that list, if at all possible. – Chris Rudd May 20 at 20:32
  • Can you not just have a scheduled task powershell up a list of accepted domains and then ensure that an alias for each domain is present? There would be no manual intervention required once its running - you may also be able to configure it to remove unnecessary aliases if domains are removed. – Semicolon May 21 at 15:13

When configuring a catch-all mailbox, we should disable recipients filtering on each server. Because messages pass through the Recipient Filter agent before passing through the Transport Rule agent, and the Recipient Filter agent will reject messages addressed to mailboxes that don’t exist. Have you enabled anti-spam on Mailbox servers? If so, disable the recipient filtering and see if issue persists. For your reference https://docs.microsoft.com/en-us/previous-versions/office/exchange-server-2010/bb691132(v%3dexchg.141)

  • I'm looking into this, is Recipient Filter only a binary option or can I configure it to still validate addresses that aren't postmaster@*? Also I noticed some places saying that if you have it enabled on a mailbox server it'll reject the entire message if ANY of the recipients are invalid, but my testing shows this might not be true (we're using only 1 server atm). We currently have it enabled – Chris Rudd May 22 at 16:28

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