Free tool
SMTP diagnostics
SMTP diagnostics checks a domain’s mail server live: it looks up MX records, connects on port 25, reads the banner and ESMTP extensions, and checks STARTTLS plus whether SPF and DMARC are published.
Step 1–4
How it works
- 1
Enter the domain to test.
- 2
We find the MX and connect on port 25.
- 3
We read the banner, ESMTP extensions and check STARTTLS.
- 4
We show SPF and DMARC status.
FAQ
What is STARTTLS?
A command that turns on encryption for the SMTP connection. Support for it signals a properly configured server.
Why check SPF and DMARC?
Without them mailbox providers can’t confirm the domain is allowed to send, so mail lands in spam more often.
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