Email Server Setup - Final Set-up and Testing

After you’ve gone through and checked the above things as well as followed whatever instructions are applicable for your server, you now need to begin the process of testing the server. This should begin with clients behind your firewall and sending only to addresses hosted on your domain. Simply set up an email client to connect to your server as the SMTP server and try sending a message to some account on your server. Then, try checking that account to see if the message went through. 

If it did, you know you have the basic functionality working on your server.  Proceed then in small steps by opening ports to the Internet and try sending mail to other domains as well as receiving mail from other domains.  If you have problems with any of these, stop and check settings to make sure the server is set up correctly, that your DNS is up and working and that your client is configured the way you want it in order to do what you want it to. Also, it would be a good idea to go to ordb.org and run an open-relay test on your server, just to make sure that your SMTP server is properly secured. 

Sendmail Tips

Sendmail is one of the most popular email servers on the Internet.  It was one of the first email servers in wide deployment and still is used on a large proportion of email servers, primarily in Unix environments. It is also notoriously difficult to configure correctly and get working. For instance, if you try to comment a line in the configuration file, the parsing engine will still expand the line and try to run it. 

Another point is to make sure to put all the MAILER() configuration lines at the end of the config file. The MAILER() lines determine what types of mail the server will send. Many of these lines also have a specific order in which they need to come. You should also make sure that you have all the FEATURE lines loaded to prevent relaying for hosts off of your network.  These are FEATURE(relay_hosts_only) with allowed hosts listed in /etc/mail/relay-domains and FEATURE(relay_entire_domain) which relays all hosts from a specific domain(s) listed in /etc/mail/relay-domain. 

Another relay option is FEATURE(relay_based_on_MX) which will relay mail from domains whose MX records that are directed to your server.  You can also set your server to reject mail from the servers listed on the Relay Black list maintained by mail-abuse.org by using the FEATURE(dnsbl).