I have an exchange 2007 server and a ISA server. The ISA server has the necessary edge transport role installed and all has been working well for a few years now.
Lately, I have noticed that theres a delay in delivering incoming messages. In the queue viewer on the ISA server, I can see the messages in a queue which is bound for the exchange server. But I also notice a lot of strange undeliverable messages in there.
I have attached a screen dump for examples. When I delete them, mail flows again.
I find it strange because its like the ISA box cant see the exchange server. DNS is functioning correctly.