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Mailcow vs Citadel: catalog facts
Mailcow	Citadel
Free Free and open source, self-hosted.	Free Free and open source under the GNU GPL, with no paid edition.
Linux, Self-hosted	Web, Self-hosted
Docker packaging makes deployment and updates more manageable Includes a full web admin panel and SOGo webmail out of the box	Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features
Requires Docker and server administration knowledge to run Resource requirements are higher than a single lightweight mail daemon	The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server
Self-hosted	Self-hosted
Open source	Open source
License not stated	License: GPL
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 October 2, 2026

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