TMG blocking connections to Exchange

[neonetman]

I've been notified that a number of emails are struggling to get to our mail server. Our ISP reports that the logs show a lot of re-try messages on the SMTP queue.

 

I suspect it is an issue with our Forefront TMG, however I'm struggling to identify exactly what the issue is.

 

Have any of you come across this issue, or have any clues on what could be the cause?

 

Cheers