Mailtrap Local

Runs on your laptop, catches every email your app sends, and gives you
a web sandbox to browse, search, and inspect them in. One self-contained
binary.

Point any app at SMTP 127.0.0.1:3535. Open http://127.0.0.1:3550 to
search and inspect HTML, text, raw source, headers, and attachments.
The same port serves a REST API - existing clients only need a host
override. Includes HTML email-client compatibility checks, categories,
release to production SMTP, and outbound webhooks.

Not a team tool: no accounts, no auth, no shared sandboxes. SQLite only.
Localhost only. Complements hosted Mailtrap; it is not a Sandbox
replacement.