Configure Postfix For Relaying to Office 365

To configure our Postfix server for relaying emails through smtp.example.com, we run

postconf -e 'relayhost = YOURDOAMIN.mail.protection.outlook.com'
postconf -e 'smtp_sasl_auth_enable = yes'
postconf -e 'smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd'
postconf -e 'smtp_sasl_security_options ='


Our username (someuser) and password (howtoforge) for smtp.example.com must be stored in /etc/postfix/sasl_passwd, therefore we do this:

echo "YOURDOAMIN.mail.protection.outlook.com  USERMAIL:PASSWORD" > /etc/postfix/sasl_passwd

/etc/postfix/sasl_passwd must be owned by root, and noone else should have read access to that file, so we do this:

chown root:root /etc/postfix/sasl_passwd
chmod 600 /etc/postfix/sasl_passwd

Now we must convert /etc/postfix/sasl_passwd into a format that Postfix can read:

pico main,cf
setgid_group = postdrop
sendmail_path = /usr/sbin/sendmail

postmap /etc/postfix/sasl_passwd

This will create the file /etc/postfix/sasl_passwd.db.

All that is left to do is restart Postfix:

mkfifo /var/spool/postfix/public/pickup
/etc/init.d/postfix restart

That's it. You can now test by sending emails over your mailserver and having a look at your mail log. You should see that all your emails are now passed on to smtp.example.com (except the ones that have a local recipient).