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Postmark Spam Check vs Mailpit: catalog facts
Postmark Spam Check	Mailpit
Free Provided free by Postmark.	Free Free to download and run.
Web	Web, Self-hosted, Command line
Quick SpamAssassin score without running SpamAssassin Usable in the browser or through a JSON API	Single binary or Docker image with no dependencies HTML compatibility, link and spam checks built in
Only gives a SpamAssassin score, not a full deliverability test Messages are sent to a third-party service for checking	For testing only, not a real mail client Spam scoring relies on a SpamAssassin setup
Web application, Hosted service	Downloadable app, Self-hosted
Closed source	Open source
License not stated	License not stated
Not stated if an account is needed	No account needed
Needs internet	Works offline
Official website Full listing and sources Checked September 23, 2026	Official website Full listing and sources Checked September 24, 2026

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