SBS Box hosting two SMTP domains


Running SBS 2011 box with two SMTP domains for email.  I want to configure smart hosts. One for each domain, the smart host for each of the two domains is different. How do I set this up

Presumably I will be filtering on the senders email address and directing to the appropriate smart host. This is something I've not done before.

Thanks for help
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Adam FarageConnect With a Mentor Enterprise ArchCommented:
Actually... Exchange 2010 can do this as long as the second domain is internal. It is called an Internal Relay:

The way this would work is that you would have as the local domain that is hosted within SBS, and then an internal relay domain which is that is a separate solution.

If emails come into, the transport service will perform a lookup and notice that it is an internal relay based off the SMTP FQDN, and then forward this through without an issue.
Adam RayCommented:
So you have two domains, and

You want to route to different smarthosts based on what email address the message is coming FROM?

I.E. userone has a primary email address of and email should be sent through smarthostone.
usertwo has a primary email address of and email should be sent through smarthosttwo?
Amiga-2000Author Commented:
That's it exactly. Thanks
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Adam RayConnect With a Mentor Commented:
Exchange 2010 (SBS 2011) does NOT have that functionality built-in. -- You can route through various smart hosts based on the recipient's/TO domain, but not the sender's/FROM domain.

A quick Google search came up with this third party app as a solution.

Disclaimer: I've not used this software or anything from this vendor before. So I am not recommending it, Google is.
Adam RayCommented:
My knowledge of internal relays isn't complete, so correct me if I'm wrong. But that would only route inbound email through the internal relay to complete delivery, correct?

When a user sends an email Exchange verifies the user has send-as permissions for that address and then sends it to the Outbound SMTP Connectors to be sent. (In this scenario they are sending email FROM TO, not TO

**This is all happening on a SBS2011 box in this scenario, so I'm simplify the process a bit.--The Exchange server houses all role, i.e. no separate edge connectors.**
Amiga-2000Author Commented:
Hi experts. Thanks for info. As both are external I'm not sure this would work.

I've spoken to the Smart host admin and they can let me use a single for both domains so I've dodged a bullet :)
Amiga-2000Author Commented:
Adam FarageEnterprise ArchCommented:
Hi experts. Thanks for info. As both are external I'm not sure this would work.

Oh, then in theory WCLLC is correct. If you had internal, you can in fact forward (using an internal relay) off to a domain that is trusted outside the network. Also, you can do the same thing through most smarthosts (its called intelligent routing most of the time, varies from product to product).

But basically the internal relay is how we use a split SMTP namespace between Exchange on-prem and O365 for a customer. Works wonders.
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