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About the SMTP Server Test

Connects to a mail server — or to the main MX host of a domain — reads its greeting, sends EHLO and, when STARTTLS is offered, upgrades the connection to report the TLS version and certificate. It never sends a message.

• The greeting banner and every EHLO extension
• STARTTLS support, TLS version and certificate
• Port 25 (server to server) or 587 (submission)

Frequently asked questions

Which SMTP port should I use?

Port 587 with STARTTLS for sending mail from a client, or 465 for implicit TLS. Port 25 is for server-to-server delivery and is blocked by most consumer ISPs.

Does this test send an email?

No. It stops after the greeting, EHLO and (when offered) STARTTLS, then says QUIT.

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