We have a Distribution Group set up, which contains a mixture of recipients : normal internal addresses, and external addresses which have previously been set up as Contacts. If I email one of the Contacts direct, they get my email. However if I email the Group, the Contacts don't get it. Any ideas folks? I found this KB article Messages that are sent through Exchange 2003 to an external messaging server are blocked by Sender ID checking whose first bullet point sounds like the same issue. What do you think?