I have used Forefront on Exchange many times in the past on Exchange 2007 and 2010. I am getting this warning relating to smtp in the App log.
Event ID 2064 - Unexpected SMTP server response. Expected: 220, actual: 500, whole response: 500 5.3.3 Unrecognized command
I found the article below which addresses this supposedly. I was a little concerned about creating another Receive Connector in Exchange just for Forefront. I never had to do this in the past. Yes, our default RC does have anonymous enabled. I need it this way to accept inbound emails just like the article states. Was wondering if anyone else ran into this problem and found another way to resolve it? It appears to be an issue with Forefront on the MB server trying to send notifications using the CAS. I am not getting any email alerts from the MB servers regarding scanning, updates etc.....