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OpenSMTPD vs Exim: catalog facts
OpenSMTPD	Exim
Free Free and open source under the ISC license.	Free Free and open source under the GNU General Public Licence.
Linux, Self-hosted, Command line	Linux, Self-hosted, Command line
Part of the OpenBSD project Simpler than many other SMTP servers	Very flexible mail routing Extensive checks for incoming mail
A mail server, not a client for reading email Needs other components for a complete mail setup	Configuration is complex and differs from Sendmail A mail server, not a client for reading email
Downloadable app, Self-hosted	Downloadable app, Self-hosted
Open source	Open source
License: ISC	License: GPL
No account needed	No account needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 24, 2026	Official website Full listing and sources Checked September 24, 2026

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