Postfix Hardening for MX Guarddog
For this guide, the following assumptions are made:
- MX Guarddog is being used to filter spam
- MX records have been set to MX Guarddog's servers
- Postfix successfully receives and delivers mail from MX Guarddog's servers
After following the instructions at MX Guarddog for setting up the MX records, email addresses, email server, and quarantine reports, everything should Just Work™. Spam should slow to a trickle; MX Guarddog does a really good job of spam filtering! The only thing they can't protect against is spammers that ignore the MX records of a server and try to connect directly to the server. For that, some configuration will need to be done. In addition to this, we'll also prevent submitting email on port 25 and only allow it on the submission port (587).