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Stalwart vs Mail-in-a-Box: catalog facts
Stalwart	Mail-in-a-Box
Free Free and open source, self-hosted.	Free Free and open source, self-hosted on your own server.
Linux, Self-hosted	Linux, Self-hosted
Modern JMAP support alongside traditional IMAP and SMTP protocols Rust implementation aims for security and performance	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
Requires self-hosting and server administration knowledge Newer project with a smaller ecosystem than long-established mail servers	Requires comfort running and maintaining a Linux server Tied specifically to Ubuntu, limiting deployment flexibility
Self-hosted	Self-hosted
Open 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.