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
pmta reload
The heart of PowerMTA lies in the domain directives. This is where you tell the software how to handle specific receivers (like Gmail, Outlook, or Yahoo). powermta configuration guide top
The Golden Rule: Do not use a "catch-all" configuration for critical ISPs. You must create specific domain keys for major providers. When an ISP returns a "Try again later"
<domain gmail.com>
max-smtp-out 20 # Gmail limits concurrency per IP.
max-msg-rate 10/s # Respect Google's rate limits.
max-msg-per-connection 50
use-starttls always # Force TLS for security.
require-starttls true
dns-timeout 15s
initial-pts 30
max-pts 3600
pts-expiration 5m
# Feedback loop support
dsn true
</domain>
Shows queues, active connections, and rate limits in real time. pmta reload The heart of PowerMTA lies in
$ pmta status
Virtual MTA 'main':
Active: 45 connections
Queue: 12,340 messages
Rate: 23.4 msg/s