How to route internal Exchange mail through external servers

Question

I have a client (lets call them Contoso Ltd. with the domain contoso.com) who I have just deployed SBS 2011 for their head office.

Due to a contract they are committed to using a 3rd party POP email host as their primary mail server.

I set up Exchange 2010 to use POP connectors for the 30 domain users in the office. All is good.

Today all of a sudden I was told they have a further 100 users in the field that just use POP accounts with the same host.

The problem is internal email, when someone in the office email john@contoso.com and exchange cannot find the AD user it bounces it back to the sender evan though john@contoso.com exists on the POP mail server.

The people on the office want to continue using Exchange. The people in the office and in the field need to use the contoso domain and cant use another domain. Contoso cant afford the SBS2011 User CALs for another 100 users and SBS can take Max 75 users.

I would love a way of setting the internal connectors to route emails to people not on the domain via the external server, if not, all internal email via the external server. Its not a problem POPing the mail back down.

THANKS GUYS

Answer 1

You can do this by switching the domain contoso.com from authoritative domain to internal relay domain in the accepted domains list in Exchange management console > organization configuration > hub transport > accepted domains.

For domains listed as authoritative Exchange assumes all the addresses in that domain are known inside Exchange but for domains listed as internal relay Exchange reroutes emails to addresses not known are routed out to the internet while emails to addresses that are known inside Exchange are delivered normally.