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How to block in comming email to internal Exhange 2007 and Exchange 2003 distribution groups?

355LT1
355LT1 used Ask the Experts™
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I have an large Exchange Eniviorment with Exchange 2007 HT and Exchange 2003 MBX servers.
How can I easily block external email  sent to to internal distribution groups. Note I have to manually block several hundred DLs from recieving email from the outside.
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Benjamin MOREAUProject Manager

Commented:
You can select the checkbox "Require that all senders are authenticated" on your distribution group. So, you will block all external mail on your Distribution Group.

Read this for more information : http://technet.microsoft.com/en-us/library/bb397214(v=exchg.80).aspx

You can script this with powershell to block a lot of Distribution Group.

Author

Commented:
Is there away to do this for all distribution groups.
Project Manager
Commented:
Yes. You can do something like this :

get-distributiongroup | set-distributiongroup -RequireSenderAuthenticationEnabled $True

So, only authenticated user (=internal users) will be able to send mail to all DG