Ask the Expert

Unresolved recipient issue between an Exchange server and a virtual server

I am using two mail servers for my company: a Microsoft Exchange server inside the LAN and another mail server managed by a third-party for our company. Both servers are sending e-mail to ''

If an Exchange server user,, sends an e-mail to on the other server, user1 gets a reply that the message was not delivered and that there was an unknown user (the Exchange server is looking for user2 and user2 is on the other server).

How can I solve this problem?

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View the properties of the SMTP Virtual Server on the Exchange server. Go to the "Messages" tab and fill in the dialog entitled "Forward all mail with unresolved recipients to host" with the address of the external server.

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Related information from

  • Tip: Dealing with undeliverable messages in Exchange Server
  • Tip: Common Exchange mail delivery issues
  • Reference Center: Non-delivery reports tips and resources
  • This was first published in May 2006

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