Question:

Can someone tell me how to block external email from going to our company email adress

Its one email we created when one person wants to email the entire company

Answer:

Are you trying to prevent internet recipients from sending mail to a
distribution group that includes all company employees?

If running Exchange 2003,

go to the Exchange General tab of the distribution group in ADUC and
click Delivery Restrictions, place a check in the box “From Authenticated
Users”.

Only internal users can send mail to the DG now.

If using Exchange 2000, you will need to create a fake email address for the
DG. You can do this manually or by using a Recipient Policy

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