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Poste.io vs Mail-in-a-Box: catalog facts
Poste.io	Mail-in-a-Box
Freemium Free for personal use with paid licensing for larger deployments.	Free Free and open source, self-hosted on your own server.
Linux, Self-hosted	Linux, Self-hosted
Single Docker container simplifies deployment of a full mail stack Includes web admin, webmail, and TLS handling out of the box	Automates the entire setup of a mail server stack on a single Ubuntu box Open source, so the full setup can be audited and self-hosted
Free tier is limited, with paid licensing for larger deployments Requires Docker knowledge and a server to run	Requires comfort running and maintaining a Linux server Tied specifically to Ubuntu, limiting deployment flexibility
Self-hosted	Self-hosted
Closed source	Open source
License not stated	License not stated
Not stated if an account is needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 22, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.