Group, I've installed the ISA Server Feature pack to take advantage of the AUTH feature in the SMTP Filter. That feature works well, however, since installing I have found a few domains out there that are not able to send mail to my exchange server. There are only 2 I have found since Feb, but they are experiencing "connection" problems when sending mail to my domains. I can send to them, they cannot send to me. Are there any additional measures I can take to investigate this? It seems like they have unorthodox firewall configs that are causing this, but it is becoming a problem for my clients. Thank you for the info, Russ Highton Jr.