Blocking emails for certain addresses

We have recently migrated a large number of users from third party systems to our central Exchange platform, but have issues with people still using old email addresses within head office.

For example, we moved our training department from old AOL based addresses to the Exchange system with the same format addresses as all head office staff - but some people insist on using the AOL addresses still - probably those where Outlook remembers them when typing a name in.

How can we block emails to these addresses sent from our Exchange system and then have an error message sent back to the sender?  This should remind them to use the new addresses in the address books as most are ignoring our reminders.
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Please clear Outlook .NK2 files from user profiles [C: D:\Documents and Settings\USER\Application Data\Microsoft\Outlook], so that old addresses are not remembered. And make sure old Addresses are not visible in GAL.
Also, if there is any specific domain, then in the SMTP Connector block that domain. Else create another SMPT Connector and in Address space only keep that Domain like and give it higer priority so that for that mail go via that connector only and for others the default is used. And in bridgehead give an invalid IP
Let me know if you understood
Nitin Gupta (gupnit)

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Not 100% if this will work - you would have to test first:

If you don't want to block the entire AOL domain from being impacted, you can add the specific AOL addresses as Contacts in AD.  Then on the Exchange General tab, in the Message Restrictions area, check the button, "Only from:".  That may prevent your users from sending to those particular addresses.

Sorry, but I can't test this out in our environment.  If it does or doesn't work, I would love to hear back.

gupnit...that's a neat trick! Gotta remember that one.
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