I have simple server Windows 2008 Standart SP2 with Exchange 2007 with apply SP1. Only one DC and one Exchange server (not exist Edge) in the same server.

I have first distribution group by name "[email protected]" with 10 users. Working with internal and external mail correctly.

I have second distribution group by name "[email protected]" with 3 users. Working with internal mail correctly, but external mail delivery failed 2 from 3 users. Only 1 users proclaims that external mail delivered correctly. Those 3 users they are too member of distribution group [email protected]" .

I am not found in the eventlog any problem with Exchange server. Any user and any distribution group not check the box "Require that all senders are authenticated."

Any ideas on how to solve the problem?