Why isn’t port 25 tested?

SMTP test

Does the mail server answer, offer encryption and present a valid certificate?

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Good to know: Tests the submission ports (587 and 465) that mail apps and services use to send. Server-to-server port 25 isn’t tested.

About the SMTP test

Connect to a domain’s mail server, read the banner, test STARTTLS and check the certificate on the submission ports.

Every result comes in two styles: plain English for everyone, and the exact technical detail for engineers, with the raw JSON one click away.

Questions

Port 25 is server-to-server delivery, and most cloud networks block it to stop spam. This test checks the submission ports (587 and 465) that mail clients and apps use.