First of all: Sending and receiving, inbound and outbound works fine. The problem I have is, that I've created a rule in Outlook 2003 that forwards any incomming message to an email address outside the organisation. When an email arrives I see in the Message Tracking Center that the server tries to handle the forward, but the last event is "SMTP: Message submited to Categorizer".
When I change the rule to forward the message to an internal email address it works fine. Also when I not use an Outlook rule but set the delivery option in the active directory for that user to forward mail to an external email address it works fine. Just with an Outlook rule it stucks.
The mail is not shown in any Queue and I also disabled the whole AV software.