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Port & Mail Server Connectivity Tester

Opens a direct TCP connection to the common mail, web and sysadmin ports on a host, grabs whatever banner the service volunteers, and checks whether the plaintext mail ports advertise STARTTLS. Note: many hosts (including most shared/cloud hosting) block outbound port 25 entirely, so a closed 25 here can reflect this checker's own network rather than the target server.

📖 Guide: Mail & web ports explained

Last updated: September 9, 2026

How to use this tool

1. Enter a hostname (usually your mail server) and click Check.
2. Add a custom port if you need to test something outside the standard mail/web/sysadmin set already checked.
3. Look for STARTTLS support on the plaintext mail ports (25, 587, 143, 110) — its absence there is a real finding, not noise.
4. A closed port 25 from this checker alone isn't conclusive — confirm from another network too, since many hosts block it outbound regardless of your own server's configuration.

Use it when mail delivery is failing or slow and you need to rule out a blocked or misconfigured port before chasing DNS or authentication issues instead.