- Multi-tenant isolation (one bad customer does not affect others)
- High-volume parallel delivery
- Smart bounce classification
- Feedback loop integration
- Commercial MTA features without commercial licensing
# PostMTA config for 100K/day volume
log {
sampling {
everything 1
open_connections 100
}
}
listen 0.0.0.0:2525 {
relay_hosts ['0.0.0.0/0']
}
queue_run [
label 'default'
throttle '200/second'
]
When to Use Each
Use Postfix for: internal mail, mail relay, any system where volume stays under 10K/day.
Use Exim for: shared hosting management, complex routing requirements.
Use PostMTA for: transactional email, marketing campaigns, anything above 50K/day, any system where sender reputation matters.
The Migration Path
Migrating from Postfix to PostMTA for a high-volume system:
- Install PostMTA alongside Postfix on the same server
- Configure PostMTA with your sending domains and DKIM keys
- Point your application at PostMTA port 2525 instead of Postfix port 25
- Run both in parallel for 48 hours to verify delivery rates
- Decommission Postfix once PostMTA is stable
PostMTA configuration is dramatically simpler than Postfix for high-volume use cases. The learning curve is shallow for the first 80% of features and steep only for advanced multi-tenant configurations.