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HELO vs smtp4dev: catalog facts
HELO	smtp4dev
Paid Sold as a paid desktop application.	Free Free to download, with the source code published on GitHub.
macOS	Web, Self-hosted
Local SMTP server that catches mail before it reaches real users Automatic broken link check	Captures outgoing email so test messages never reach real inboxes Web interface for inspecting captured messages
Paid only Laravel Herd Pro now includes its own email testing tool, which overlaps for PHP users	Meant for development and testing, not for sending real mail Documentation lives mainly in the repository
Downloadable app	Downloadable app, Self-hosted
Closed source	Closed source
License not stated	License not stated
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.