SMTP server check with STARTTLS diagnostics

How to use this tool

Enter a mail server hostname or public IP and choose a port. On port 25, a domain with MX records is checked through its preferred mail exchanger. Port 465 begins with TLS; ports 25 and 587 can negotiate STARTTLS when advertised.

Reading the results

The check reads the greeting, sends EHLO and, when available, negotiates TLS before quitting. It never authenticates or sends mail. Firewalls and hosting policies may block the connection. A certificate mismatch is reported rather than bypassed, especially when checking an IP instead of the certificate’s hostname.