Postfix Configuration Settings for Ubuntu and Debian

1. Install Postfix:
   This will remove exim since there can't be two mail systems active at the same time.
   If you have a website, choose "Internet Site" when the configuration prompt ask for it.
   

   apt-get install postfix
   

2. Verify mail.log to see if postfix started correctly.

   cat /var/log/mail.log
   

3. Add your domain to the config files, so others can't abuse your mailsystem.

   postconf -e "myorigin = example.com"
   

4. Add your hostname (computer name).
   Use command "hostname" at the command-line to display your hostname if not sure.

   postconf -e "myhostname=server1.example.com"
   

5. Now add the domain names that your system will handle.

   postconf -e "relay_domains= example.com, example2.com, example3.com"
   

6. Reload the Postfix server:

   postfix reload
   

7. Test the mailserver.

   telnet localhost 25
   

You should see something similar to:

Trying 127.0.0.1...
Connected to localhost.localdomain.
Escape character is '^]'.
220 server1.example.com ESMTP Postfix (Debian/GNU)

8. Try sending an email:

   mail from: < you(at)youremail.com > 
   rcpt to: < user(at)example.com >
   data
   To: user(at)example.com
   From: you(at)youremail.com
   Subject: Hey my first email
   This is my first postfix email after installing and configuring it.
   It was easy.
   .
   

Make sure to add an extra '.' at the end to indicate the end of the email content.
Use "quit" to return to the regular command prompt input.