CRM 4.0 Email Router: Emails from internal AD adresses won´t show up in queue (from some users only)

I use CRM 4.0 and the email router. We have a support queue which is running fine for external emails. But from most of our internal AD users the emails won´t show up. In the exchange email inbox all the mails are showing - it is just that some don´t appear in the queue.
So I gave the "not working" users the role of the "working" users - no success!
I tried to use everytime the outlook client - no success!
Emails directly sent from inside from outlook without client - no success.
ALL emails from the outside work!!
So where is my mistake??