Harden Postfix on Slackware (base)

1. Goal

Tighten Postfix SMTP behavior while preserving the intended relay or delivery role.

2. Files and components involved

/etc/postfix/main.cf
/etc/postfix/master.cf
/var/log/maillog

3. Operational flow

set mynetworks minimo
reject_unauth_destination
disable vrfy
riload postfix

4. Operational verification

postfix check
postconf -n
tail -n 50 /var/log/maillog

5. Practical notes

Apply these changes during a maintenance window and keep a backup of the original files for a quick rollback.

Tightening a policy without an alternative access path is the fastest way to lock out legitimate users as well.

Quick checklist

[ ] Backup or copy of the existing configuration completed
[ ] Files and commands updated as expected
[ ] Local test completed successfully
[ ] Logs or final output verified
[ ] Rollback procedure documented

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