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Citadel vs Apache James: catalog facts
Citadel	Apache James
Free Free and open source under the GNU GPL, with no paid edition.	Free Free and open source from the Apache Software Foundation.
Web, Self-hosted	Self-hosted
Mail, calendar, contacts, forums, wiki and chat in one server Consistent rooms-based structure across features	Supports modern JMAP alongside SMTP, IMAP and POP3 Mailet container for custom mail processing
The rooms metaphor differs from conventional mail servers Requires running and maintaining your own server	Requires a Java runtime and some server administration knowledge Distributed setups depend on extra services such as Cassandra
Self-hosted	Self-hosted
Open source	Open source
License: GPL	License: Apache-2.0
Not stated if an account is needed	No account 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 October 2, 2026

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