Powermta Configuration Guide Top
When an ISP returns a "Try again later" (400-series) error, PowerMTA enters a back-off mode. Configure this carefully:
# Global settings or specific domain
retry-interval 5m # Wait 5 mins before retry
max-retries 10 # Give up after 10 tries
Allocate huge pages for queues:
queue-mem-pool-size 2048M
large-message-threshold 262144 # 256KB
If you cannot measure it, you cannot fix it. PowerMTA’s logs are in /var/log/pmta/. powermta configuration guide top
This defines how many total outgoing connections PMTA will make. Start here.
max-smtp-out 500 # For a mid-tier server (4 vCPU, 8GB RAM)
# Warning: Do not exceed 2000 without kernel tuning.
PowerMTA (by Port25) is the industry standard for high-volume email delivery. Unlike standard MTAs (Mail Transfer Agents), PowerMTA is built specifically for commercial sending, offering granular control over delivery speed, bounce processing, and reputation management. When an ISP returns a "Try again later"
However, installing PowerMTA is only the first step. To maximize inbox placement and throughput, you must configure the config.dat file correctly. This guide covers the top configuration settings you need to master to ensure stability and high deliverability.
<domain gmail.com>
<limits>
throttle 1000/hour
error-throttle 500/hour on 4xx,5xx
defer-throttle 200/hour on 421,450
</limits>
</domain>
error-throttle reduces sending when ISP rejects (hard bounce), defer-throttle cuts rate on soft errors. If you cannot measure it, you cannot fix it
If a remote mail server is silent, kill the connection.
host-command-timeout 120s
