Hi, our LAN (NT4 SP6a clients) is connected by a linux (SuSE 7.0) firewall (SuSEFirewall 2.6) and proxy (Squid 2.3.3) to the internet. We have a mail server (on an NT machine), which kicks the mails with the ETRN command from our ISP. After connecting to the ISPs mail server the connection is reset by peer (winsock error 10054). Without the firewall, everything works fine! This problem seems to occur, because our mail server sends UDP packages to the ISPs mail server. These packages are blocked by the firewall. Then, the firewall sends back ICMP port unreachable packets, which reset the connection. In the firewall logs, I can not determine any denied packages?! My questions: 1. What/Why UDP packages/ports? 2. Does every mail server use UDP packages in order to kick mails? 3. Other error? Because nothing is logged. Thanks CU Sven