Mail Routing to different servers

attractsupport used Ask the Experts™
We are in the process of setting up a hosted exchange server and would like to offer our customers the ability to use the service for a few users while have other users utilize our standard hosting service with pop3 access.

Can exchange handle this type of routing.
IE, email comes in, either routed to exchange or to a different mail server?
if exchange can not do this, what software (preferably open source) could do this?

thanks for your help
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Exchange can handle this, but you are likely better off using either a third party gateway (like Mimecast) to make routing decisions or installing a gateway server that can make those decidions for you.

Remember, you have another major problem with this type of scenario...
Exchange does not know about non-Exchange users who are on the same domain, so users who are on your hosted Exchange that want to send to a user who is not will have problems. Exchange will BOUNCE this message. In order to stop that happening you will have to create a mail enabled contact (forwarding address) for every single external user.
Your gateway should then re-write the addresses of the mail enabled contacts so that they get delivered to the right place.

Any linux gateway will handle this for you. My choie would be postfix.

Alternatively you could try to use the "fall back" transport. This sends ANY unknown recipient mail to another location. Might be your gateway. You will have to be careful as this might be a global config and not scale for your hosted environment.
I agree - forwarding mail out of exchange is lame-

however, Exchange can accept mail for multiple domains. THat said, it really is best to keep distinctly differen mail domains.  I would use the hosting service if you dont want to deal with the hassle of running your own mail organization. There is an exchange hosting service that integrates well with native exchange this is the same service that is being sold with SBS foundation essentials.

I hope this helps


Thanks for your replies.
While i do not know which way we will choose to go, these answers are great!

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