Hi, I have a single Exch 5.5 server published behind ISA for SMTP and POP3. All DNS records have been checked and are OK as this server was OK with POP3 before it was behind ISA. Previously it had its own ISDN direct connection. (Hence the need for a firewall!!) SMTP works fine for local users. External users connecting to the net can not use pop3 to collect/send mail. I've read through a lot of infomation here and really want someone to confirm that we should roll out the firewall clients to solve this issue. Or is there something we may have missed. Please can someone help. Thanks Brian