Postfix SMTP relay and access control

Introduction

The Postfix SMTP server receives mail from the network and is exposed to the big bad world of junk email and viruses. This document introduces the built-in and external methods that control what SMTP mail Postfix will accept, what mistakes to avoid, and how to test your configuration.

Topics covered in this document:

• Relay control, junk mail control, and per-user policies
• Restrictions that apply to all SMTP mail
• Getting selective with SMTP access restriction lists
• Delayed evaluation of SMTP access restriction lists
• Dangerous use of smtpd_recipient_restrictions
• SMTP access rule testing