Exchange migration tips - changing the outbound delivery mechanism
Remember that with Exchange 5.5, in order to send or receive Internet e-mail, you had to install the Internet Mail Connector (IMC) a.k.a Internet Mail Service. Exchange 2000/2003 no longer require (or use) an IMC to send/receive internet mail, as they use SMTP natively and have the ability to send/receive e-mail from the internet by default. That being said, you might expect that once you introduce an Exchange 200x server into your org, that it would send outbound mail itself. Not so, my friend. Instead, your Exchange 200x server will, you guessed it, still use the 5.5 IMC for outbound e-mail. If you want to change how outbound e-mail routes, then you must make some configuration changes.

There are basically 3 different methods that should allow you to change how outbound e-mail is routed.
1. Rename the address space on the IMC to something invalid (i.e. bogus.local). Install an SMTP Connector on an Exchange 200x server with the address space of "*". There are a few more steps that need to be done - for that, make sure to reference the KB article I have linked to at the bottom.
2. Remove the address space on the IMC. Obviously, removing something is inherently a "bit" riskier, but in this case, should pose no problems. Once the address space is removed and replicated, you would do the same as above with installing and SMTP connector.
3. Add an SMTP connector with a lower cost that contains the same address space (i.e. "*"). While theoretically the connector with the lowest cost ought to win, I've heard reports that it doesn't necessarily always work that way, and that the IMC "may" still win. The best thing to say about this is YMMV (Your mileage may vary). If it doesn't work, then revert back to either of the previous methods.

Once you have chosen a method, and verified that outbound e-mail is now routing through the Exchange 200x server's SMTP connector instead of the IMC, you can safely remove the addres space (if you didn't already) and then once replicated, you can uninstall the IMC. As I mentioned earlier, there is a terrific MSKB article that references how to do this. That article can be found here.
How to switch outgoing mail connectors when migrating to Exchange 2000 or 2003
- posted by Ben Winzenz @ 1:56 PM