Debian Resources

Postfix as Outbound Mail Relay with Authentication

Since I use mutt, the component that deals with SMTP is my local Postfix. It doesn't know about SMTP AUTH yet, but we only need two additional options in main.cf
nano /etc/postfix/main.cf
relayhost = smtp.example.com
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

The first directive enables SMTP AUTH in Postfix's SMTP client component. The second dictates which username and password to use when talking to each server. A sample sasl_passwd map looks like this:
nano /etc/postfix/sasl_passwd
smtp.example.net________username@example.com:your-password
192.168.1.1____________ username2:geheim

Don't forget to create the hash of the map by using postmap /etc/postfix/sasl_passwd. Now point your relayhost variable to one of the servers listed in sasl_passwd and reload the Postfix configuration. Mail relay should now be using SMTP AUTH. If the login fails, check for the presence of the libsasl2-modules package. Without it Postfix will try to use authentication, but will fail because no suitable authentication methods can be found.
/etc/init.d/postfix reload

One Word About Encryption
Although I didn't show how to configure encryption in this example, I strongly suggest using TLS with every MTA you run. The setup isn't too hard and having encrypted SMTP AUTH sessions is the best way to protect the passwords.
chmod 600 /etc/postfix/sasl_pass*