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I have o365/Exchange configured as an internal relay, so it sends incoming mail for which there is no mailbox onwards to a smart host. The smart host only handles email for addresses prefixed with "otm-".

However the problem is that NDRs aren't generated in this configuration.

I have tried to solve this by making o365/Exchange authoritative for the domain and configuring a rule to redirect only incoming email with the "otm-" prefix in the recipient address to the smart host but I haven't been able to get this right — now everything except the main o365/Exchange mailboxes gets an NDR.

I think I have the rule correct but I think emails are being rejected before the rule is processed.

How should I go about configuring this?

  • You can have a read at this similar case, https://serverfault.com/questions/802555/relay-specific-exchange-mailbox-to-defined-smtp-host Within your organization configuration, setup a send connector for a specific domain and configure it to route mail to the ticketing system's SMTP server as the smart host. You can also read this https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/set-up-connectors-to-route-mail – Beverly Gao Sep 05 '19 at 07:50
  • Thanks but that answer covers the case of forwarding a know address by adding a contact, but not unknown addresses (prefixed with "otm-") which is what I need. The MS doc doesn't address this case, just general setup of connectors and rules. –  Sep 05 '19 at 08:37
  • Any updates with the issue? – Beverly Gao Sep 18 '19 at 08:56
  • I'm planning to make the domain non-authoritive and then generate NDRs from rules. If this works out I'll self-answer at some point, though it's a messy solution. –  Sep 18 '19 at 09:51
  • Have you made it now? Thanks for sharing. – Beverly Gao Oct 04 '19 at 09:06

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