Hi, For Exch 2003, How to block ANY external user from sending email to internal group mail. By example, External user from valid email abc@gmail.com send email to group email groups@abc.com. There is any setting need to apply at Exch 2003? Thank you. jaie

To set the value to require authentication to send to a distribution group, follow these steps: Click Start, point to Programs, point to Administrative Tools, and then click Active Directory Users and Computers.Right-click the distribution group, and then click Properties.Click the Exchange General tab.Under Message restrictions, click to select the From authenticated users only check box. When I am apply this setting, only internal user can send email to Group email? It is correct? What happen to external email? Exch will bounce back with NDR to original sender?jaie

You are correct, Exchange should send back an NDR saying that the sender does not have permissions to send to the group. Jim McBee - Blog - http://mostlyexchange.blogspot.com

Thank for the info :)jaie