It continues! As mentioned previously, I've followed the "Virtual Users And Domains With Postfix, Courier And MySQL (Fedora Core 5)" tutorial. Authentication, both plain and SSL, work fine for pop and smtp connections from within my 3 IP address block. Outside of my block, I can still receive mail with pop, but smtp hangs and doesn't send. There is no trace of an SMTP connection in /var/log/maillog in these cases. As long as I send from a system within my address block, it shows up as expected. This would suggest a firewall issue, but: Code: [root@spider ~]# iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination The only hardware between the mail server and the world is a switch and a dsl modem. I doubt the error from OE would help, but here it is: Code: Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'mail.mydom.ain', Server: 'mail.mydom.ain', Protocol: SMTP, Port: 25, Secure(SSL): No, Socket Error: 10053, Error Number: 0x800CCC0F I should probably also include this: Code: [root@spider ~]# telnet mail.mydom.ain smtp Trying 184.108.40.206... Connected to mydom.ain (220.127.116.11). Escape character is '^]'. 220 mydom.ain ESMTP Postfix ehlo localhost 250-mydom.ain 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-STARTTLS 250-AUTH LOGIN PLAIN 250-AUTH=LOGIN PLAIN 250 8BITMIME AUTH PLAIN myEncryptedInformationHere 535 Error: authentication failed quit 221 Bye Connection closed by foreign host. An update to this: the telnet above was from localhost. When trying to telnet from outside to the SMTP port, the session resolves the IP address correctly and attempts to connect, but hangs for a couple of minutes and returns a connection timed out error. Any ideas what's up with this?