Postfix can be locked down to only accept email from the MailRoute servers. Because of the wide range of possibilities for postfix configuration, please consider this a general guide, and not a hard-and-fast set of instructions.
- Edit your main.cf file. This is usually found in /etc/postfix/main.cf
- Add 18.104.22.168/21 to mynetworks
- Set smtpd_client_restrictions = permit_mynetworks, reject
- Execute postfix reload to reload the settings and have them take effect right away
Please feel free to contact us at email@example.com if you have any questions. We use postfix ourselves, and we'll do whatever we can to help.
***for OS X Servers; Add our addresses to mynetworks, change "smtpd_client_restrictions" as specified, and then restart the server. On a mac, that might require a reboot.