Rich, The ability to reply to ping (ICMP packets) has to be set (allowed) in ISA. Check technet for that. You'll have to make a rule 'ICMP ping respone (in)'. The reason why your mail doesn't come in will have to do something with the packet-filter rules or so. Check your packetfilter log, if packets are dropped. If not check firewall log and try to figure out what part of the communication is not going right. I hope if pointed out the way to look for ;-) Frederik