Originally posted by: SystemAdmin
This can get quite length for a forum as the last exchange on this topic showed.
A few key things to get you started.
1. Make sure you are working in an environment with a DNS server.
2. Make sure that host name resolution works properly in both directions
host <ip_address> gives the same as host <hostname>
nslookup <ip_address> same as nslookup <hostname>
3. By the way sendmail does not need to be running to send mail, just to receive
4. If you are sending mail through a mail gateway, then configure for this in your /etc/sendmail.cf filg.
DSsmtp:<relay address>
5. Try to send something locally and then to a remote host with the -v flag
sendmail -v user@host < /etc/motd
6. Work from output to debug your issue. Is the relay host working as a rely or has it been turned off for security reasons
550 5.7.1 <
root@host.domain>... Relaying denied