Best Self-Hosted Email Server tools by public signals

These picks are computed from scored public evidence. Use the openness column in the ranking to separate OSI-approved, source-available, open-core, proprietary, and unverified-license tools.

Use Case Rankings

Ordered by ToolVitals score, health, shipping, confidence, and then adoption as a tie-breaker.

# Tool Health Shipping Openness Stars Score Status
01 gromox
Groupware backend supporting mail and calendar protocols.
73 75 OSI-approved OSS 241 79 Warning
02 Mail-in-a-Box
Mail-in-a-Box helps individuals take back control of their email by defining a one-click, easy-to-deploy SMTP+everything else server: a mail server in a box.
74 36 License unknown 15.3k 67 Warning