email forwarding when using smart host RRS feed

  • Question

  • I was recently asked to forward a users email to an external email address. I created the contact with the external email address. I forwarded the email from the user to the contact.

    We also use a smart host for spam filtering. In Default SMTP Mail Transport properties if I select Use DNS to route to each address space on this connector the email forwards to the external address as it should.

    However, if I select Forward all mail through this connector to the following smart hosts the forwarding fails. I receive email at the user email account. I do not receive the email at the contact's external email account.

    I contacted tech support of the smart host. The forwarded email is being blocked because it's using the original senders domain as the sender and not from our user account domain.

    How can I relay all outgoing mail to the smart host and send forward email to the contact using the exchange server?

    Wednesday, November 20, 2013 4:35 PM


  • Does your smart host expect that all outbound e-mail uses your domain name in the MAIL FROM command? When you forward (an unfortunate choice of words, it should really be "redirect") a message using the Exchange server the original sender's address is used.

    Check your Exchange server's SMTP protocol log and see if the messages are accepted by your smart host. If they are then you'll have to switch to your smart host's log files to find out what happened to the messages.

    If your smart host is rejecting the message the original sender should be the person receiving the NDR. Have you checked with them to see if they are?

    It may also be that the original sender's domain publishes SPF data in DNS for their domain. Your server (or your smart host) is unlikely to be included in the set of authorized IP addresses for their domain. If the checking is using SenderID and your server is correctly populating the "Sender" or "Resent-*" headers then things should work. But if the smart host is using SPF then the message will be reected unless you've white listed your Exchange server's IP address on the smart host.

    --- Rich Matheisen MCSE&I, Exchange MVP

    Wednesday, November 20, 2013 10:47 PM