Within my organization, there are two employees with the same name, at different sites. We have changed their display names to reflect their geographic locations, but this does not prevent our users from sending to the wrong person. We need to prevent users at Site 1 from contacting the employee at Site 2. Is there a way to go about this, either by blocking Site 1's subnet / IP range from that specific recipient at Site 2? Or would this be better accomplished with a group policy to prevent outgoing mail from our site to that specific user? Any advice on this would be greatly appreciated.

You can use Transport rule on the Edge.

Hi, What is unwanted messages? What's the version of your exchange server? If you block all the users from site1 to send message to that user, all the normal messages will be blocked as well. That's mean the mailbox in site2 cannot receive the message from site1 anymore. If you use exchange 2007 or 2010 you can also create a transport rule: Condition "From people" set all the people in site1 "sent to people" set mailbox in site2 Action "redirect the message to addresses" set mailbox address in site1. http://technet.microsoft.com/en-us/library/aa995961.aspxPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.