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Citadel vs Mailcow: catalog facts
Citadel	Mailcow
Free Free and open source under the GNU GPL, with no paid edition.	Free Free and open source, self-hosted.
Web, Self-hosted	Linux, Self-hosted
Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features	Docker packaging makes deployment and updates more manageable Includes a full web admin panel and SOGo webmail out of the box
The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server	Requires Docker and server administration knowledge to run Resource requirements are higher than a single lightweight mail daemon
Self-hosted	Self-hosted
Open source	Open source
License: GPL	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 October 2, 2026	Official website Full listing and sources Checked September 22, 2026

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