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, then health, shipping, confidence, GitHub stars, and name.

#ToolHealthShippingOpennessStarsScoreStatus
01gromox
Groupware backend supporting mail and calendar protocols.
9696OSI-approved OSS25396Active
02Modoboa
Mail hosting made simple
9593OSI-approved OSS3.5k94Active
03Mox
modern full-featured open source secure mail server for low-maintenance self-hosted email
9290OSI-approved OSS5.9k91Active
04KumoMTA
The first Open-Source high-performance MTA developed from the ground-up for high-volume email sending environments.
9186OSI-approved OSS53089Active
05Mailu
Self-hosted mail server stack packaged as Docker images.
8380OSI-approved OSS7.5k82Active

Not Scored

Tracked for context, but excluded from rankings because comparable open/source-visible evidence is unavailable.