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smtp4dev vs HELO: catalog facts
smtp4dev	HELO
Free Free to download, with the source code published on GitHub.	Paid Sold as a paid desktop application.
Web, Self-hosted	macOS
Captures outgoing email so test messages never reach real inboxes Web interface for inspecting captured messages	Local SMTP server that catches mail before it reaches real users Automatic broken link check
Meant for development and testing, not for sending real mail Documentation lives mainly in the repository	Paid only Laravel Herd Pro now includes its own email testing tool, which overlaps for PHP users
Downloadable app, Self-hosted	Downloadable app
Closed source	Closed source
License not stated	License not stated
No account needed	Not stated if an account is needed
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.