SMTP Test

Connect to any SMTP server — typically your own mail server or relay — and watch the raw conversation happen live, then confirm real end-to-end delivery against a disposable test address. Credentials are sent only to the server you specify: never logged, never stored. Tests SMTP submission (587/465, with optional STARTTLS/AUTH) — it can't test raw port 25 MTA-to-MTA connectivity, since that's blocked at the platform level for all Cloudflare Workers, not just this tool.

587 and 465 auto-detect the right connection mode (STARTTLS or implicit TLS). Choose "Other" for a nonstandard port (e.g. 2525, common when an ISP blocks 587) — you'll then pick the connection mode yourself.

Port 25 is blocked here: Cloudflare's platform prohibits outbound connections on port 25 from every Worker, as an anti-abuse measure — that's not specific to this tool and there's no way around it from here. Use 587 or 465 to test your server's submission path, or test port 25 directly from the server itself if you need to confirm your host isn't blocking outbound 25.

Recipient

Always a freshly generated address at mailtest.webchecks.io, created automatically when you run the test so real delivery can be confirmed — not editable, and no relaying to any other address is supported.