A small, honest setup
Bring a public URL and an email sending domain. The supplied Compose setup runs on ARM and x86, and the self-host guide walks through the rest without a scavenger hunt.
Keep your own keys
Your installation has its own keys, people, and messages. Health information is built in, so you can tell whether Postbag is ready before a form needs it.
The same product
Cloud pays for hosting, upgrades, backups, deliverability, and fewer things to think about. Self-hosting gives you the same Postbag without hosted plan limits. You bring your own email domain; billing simply is not part of the picture.