Hello, I am new to LINUX administration and even newer to POSTFIX installation and administration. However, I have jumped into it with the intent of setting up my own mail server behind a firewall appliance. I am a convert from SBS 2003 and a new fan of this OS. However, my best efforts at configuring POSTFIX have so far failed and I am unable to send or recieve email. So, I turned to the excellent troubleshooting chapter (25) that is part of "The Book of Postfix" (see http://www.postfix-book.com/debugging.html). It provides great help and I have passed all of its recommended configuration tests, except one - attempts to ping to the outside world fail. If I ping to another machine behind the firewall (from within my net), all is fine as one would expect. I am running CENTOS 5.1 with POSTFIX 2.3.3 with an internal IP address of 192.168.25.13 behind a NETGEAR FVS318 firewall appliance. The firewall distributes from a static IP of 74.XX.XXX.XX as provided by COMCAST. The firewall has ports 25 and 110 open for the internal .13 machine. In addition, the foward and reverse DNS are set up properly (as confirmed with nslookup). NSLOOKUP returns mail.mydomain.com and my external IP address 74.XX.XXX.XX. NSLOOKUP returns 74.XX.XXX.XX and mail.mydomain.com In another check, I can telnet to "localhost 25" and to "mail.mydomain.com 25" where mydomain.com is our actual domain name as managed by network solutions. I can even telnet to relay-test.mail-abuse.org as another sucessful check. Finally, I try to email to the mail server from a client with the sample address: "email@example.com but the mail is rejected as " reason 554 5.7.1 <firstname.lastname@example.org>: Relay access denied. Other messages include 554 5.0.0 Service unavailable, and 554 5.5.1 Error: no valid recipients. When I try to send something out from the mail server, nothing happens and the mail stays in the outbox. Any assistance would be much appreciated. Thanks!