Hi,

We experienced queueing of messages and error is saying "message deferred by categorizer".

It resume to normal when we restarted transport service.

Is this related to Anti-Virus or Active Directory.?

Regards,

Jhun

Hello,

The categorizer performs recipient resolution before routing. Th issue may be related to recipient resolution.

Recipient Resolution

http://technet.microsoft.com/en-us/library/bb430743(v=exchg.150).aspx

I suggest you use message tracking to trace your messages.

Just bumping this as I had the same issue. Took me a number of issues to track this down to a bad transport agent. I wrote up my findings here: http://tecfused.com/2015/06/15/message-deferred-by-categorizer-agent/