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HELO vs Papercut SMTP: catalog facts
HELO	Papercut SMTP
Paid Sold as a paid desktop application.	Free Free and open source under the Apache-2.0 licence.
macOS	Windows, Self-hosted
Local SMTP server that catches mail before it reaches real users Automatic broken link check	Catches test emails without sending them Simple desktop interface for reading captured messages
Paid only Laravel Herd Pro now includes its own email testing tool, which overlaps for PHP users	Meant for testing, not a real mail server Desktop app is Windows-only
Downloadable app	Downloadable app, Self-hosted
Closed source	Open source
License not stated	License: Apache-2.0
Not stated if an account is needed	No account needed
Not stated if it works offline	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.