Postfix email header inspection/filtering using header_checks

Postfix allow email header inspection using regex pattern for custom mail filtering.

1. Add below configuration to /etc/postfix/main.cf.

header_checks = regexp:/etc/postfix/header_checks

2. Create the header_checks file with your regex filtering pattern.

/^(From|Sender|Return-Path):.*\.top/ HOLD Blacklisted .top domain
/^(From|Sender|Return-Path):.*@gmail\.com/ DISCARD gmail.com
/^(From|Sender|Return-Path):.*user@gmail\.com/ REJECT gmail.com

3. Create the header_checks map files.

sudo postmap /etc/postfix/header_checks

4. Restart postfix service.

sudo systemctl restart postfix

5. Monitor postfix log.

6. Use postmap -q to regex query the header_checks.

postmap -q "string" regexp:/etc/postfix/header_checks