Kolab

kolab.org · checked 9 Oct 2026

#5 · Mail Server Software

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How it plugs in

—Public API

NoOpen source

YesFree tier

Signal on Mail Server Software6.3#5 of 34

Kolab is a free and open-source communication and collaboration solution that can be run on your own infrastructure.

Pricing

KolabOpen-source product · self-hostedFree

As kolab.org lists them, checked 9 Oct 2026.

Near it

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Runs on

Web
Windows
Mac
Linux
iOS
Android

Facts

Website: kolab.org
Price: Free tier
Free trial: Not stated
Calendar and tasks: Kolab supports shared, colour-coded calendars, recurring events, time-zone support, invitation handling, to-do lists and task assignment.
Collaboration: Kolab provides shared email folders, calendars and task lists with granular access control, video conferencing and collaborative document editing.
Compliance and backup: The feature page describes Kolab as GDPR, HIPPA and PCI compliant and lists on-premise deployment and data backup.
Deployment: Kolab is packaged as containers that can run on one host or be distributed across a larger environment.
Deployment requirement: The quickstart says a publicly available non-clustered deployment requires one public IP and warns that email sending and receiving and WebRTC will not work without one.
Email: Email features include full-text search, filtering, aliases, identities, distribution lists, spam protection and PGP encryption.
Intended users: Kolab describes itself as a solution for companies and families that need to work and communicate together while retaining control over their data.
Maker: The site identifies Apheleia IT AG as the organization behind Kolab.
Paid services: Apheleia IT offers professional services subscriptions for larger organizations, including consulting, infrastructure integration, customization, migration, white labeling and training.
PGP caveat: Kolab's PGP feature article says the web client can store copies of public and private keys on the server and says true end-to-end encryption requires client encryption.
Protocols: Kolab supports ActiveSync, IMAP, SMTP, CalDAV and CardDAV for synchronizing email, calendars and tasks.
Security: The feature page lists PGP, two-factor authentication, DKIM/DMARC and spam protection among its email security features.

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