How do I Restrict Send/receive in Exchange 2007 to internal domain only

I have a client running Exchange 2007.  They have 1-2 users that they want to restrict their email account to only be able to send and receive email within the network.  They dont want these people to be able to send email to anyone outside the network nor receive any email from outside the network.  I have experience with Exchange 200/2003 but very little in 2007.  Thanks for your help.
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Well create Transport Rules to achieve the same. Basically if there are more than 2-3 users, then create a Group called DenyExternal (sth like that) and put these users in that Group. Now create TR and sliently drop mails for anyone in that group. Same for outgoing external mails from these users drop them
Some links to guide you:
Let me know if you need further help
Nitin Gupta (gupnit)

timbone101Author Commented:
I will be going onsite to attempt to implement this either today or tomorrow.  Thanks!
Cheers...all the best....!

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