vmta pool-high-volume source-hash true # Keep same IP per recipient (affinity) max-msg-rate 10000/minute bind-ip-range 192.0.2.10-192.0.2.30 # Your IPs

<source 127.0.0.1> smtp-service yes always-allow-relaying yes process-x-virtual-mta yes max-message-size 0 </source>

When IPs are fully warmed up, you can lift restrictive caps, but you should never remove them completely.

# ================================================== # PowerMTA Configuration File # ================================================== # Sample PowerMTA configuration file showcasing # high-performance and deliverability-focused settings.

: This sets an hourly volume ceiling. For warm, high-reputation IP addresses, this number can scale up significantly. For brand-new IPs undergoing an IP warming cycle, drop this value down to 200 or 500 messages per hour and scale up incrementally over several weeks. 4. The Backoff Engine ( )

Implementing a perfect configuration file is only half the battle. To guarantee your mail arrives in the inbox rather than the spam folder, ensure you meet these operational requirements:

Note: Replace IP addresses, domains, and paths with your own.

| ISP | Recommended max-msg-rate | max-connect-rate | Retry interval | | --- | --- | --- | --- | | Gmail | 80/h | 6/m | 1 hour | | Hotmail/Outlook | 50/h | 4/m | 2 hours | | Yahoo | 30/h | 3/m | 4 hours |

Microsoft relies heavily on temporary 421 SMTP deferrals to control incoming volume. If your server ignores these warnings and continues hammering their network at the same speed, your IP will be escalated to a hard 550 permanent block.

Configuring PowerMTA (PMTA) for high-performance delivery, often referred to as a "hot" or high-volume setup, requires a delicate balance between maximizing throughput and protecting your IP reputation . A properly tuned configuration file (typically /etc/pmta/config