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Restrict outbound relay domain

Restrict outbound relay domain

Restrict outbound relay domain

(OP)
Is it possible to restrict relaying outbound emails to only specified domains? If so, can you guide me through the process or point me in the right redirection?

Email from (Domain A) --> Exchange --> blocked unless sending to (Domain B)

RE: Restrict outbound relay domain

There are two approaches to this:

First:
Add the additional domains to the Accepted Domains list as External Relay type domains. Then inbound messages to your organizations with those domains as the recipient domains would then be forwarded on to them. The senders would not need to authenticate to do that. If non-authenticated users tried to relay anywhere else, they'd get a bounceback.

---------------------------
Second:
If you could reliably identify the IP addresses that DOMAINA would be using to send from, it would be easier to do this. That takes care of the initial "allowed to relay" issue, since you could create a custom receive connector to handle their inbound connections, and allow relaying of all their mail. There's nothing in the ReceiveConnector settings that will allow the receive connector to parse the destination domain to see if it's allowed (unless you added the destination domains to your Remote Domains list in Org->Hub).

From there you could create a transport rule that would look for "*@domainA.com" sender addresses on outbound emails and delete/drop them unless they were going to specific remote domains.

Dave Shackelford
ThirdTier.net
TrainSignal.com

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