In this example, any traffic destined for gmail.com will strictly adhere to a message rate of 100 per hour and apply specific DKIM signatures, ignoring global defaults.

<virtual-mta domain-specific> bind-to-source-ip 192.168.1.100 <domain example.com> max-smtp-out 10 </domain> <domain gmail.com> max-smtp-out 20 route alt4.gmail-smtp-in.l.google.com:25 </domain> </virtual-mta>

This covers the essential domain-level configuration in PowerMTA. For a specific use case (e.g., Gmail, Yahoo, custom smart host), the route , max-smtp-out , and DKIM settings become most critical.

To optimize your delivery, you should customize these key parameters for major ISPs:

Enable domain-specific logging in <source> or global log-domain :