Mailhog

A mail testing tool that acts as an SMTP server and captures every message your application sends, so you can read it in a browser instead of delivering real email. Captured mail is shown with headers, plain text and HTML parts, and a JSON API lets you assert on message content from automated tests.

Developers use it during local development to confirm password resets and notifications fire correctly without filling customer inboxes with test data.

Keeping it on your own network means no test message ever leaves your infrastructure, and the tool can be reset between runs as easily as restarting a container.