Block Exchange users from receiving external email

I currently have a group of users that are prevented from sending external email.  Is there a way I can make the same group unable to RECEIVE external email (but still receive internal email)?   Thanks.
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MontoyaProcess Improvement MgrCommented:
I believe this is what you're looking for:
Jamie McKillopIT ManagerCommented:

What version of Exchange? If you are using 2007 or above, open the Properties page for the mailbox, go to the Mail Flow Setting tab, open Message Delivery Restrictions, and check "Require that all senders are authenticated". This will only allow internal senders to email this mailbox.

pcservneAuthor Commented:
Sorry, its Exchange 2010.  So I'd have to that on a per user basis?  No way to use the existing group of users I have?
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Jamie McKillopIT ManagerCommented:
It needs to be done on a per user basis but you could script the change in powershell to do it in batch.

Lior KarasentiCommented:
Check this guide:

scroll down to the part 'How to create a rule to block a user/group from receiving mails coming from outside the company'

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Yes you can create Transport rule for the group.

Name: 'Test'
Comments: ''
Priority: '0'
Enabled: $true
FromScope: 'NotInOrganization'
SentToMemberOf: 'Group Name'
DeleteMessage: $true
pcservneAuthor Commented:
I think the post by by: liorkr will work, just haven't had time to try it yet.
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