SMTP server check
Enter a domain to test each of its mail servers on port 25, or a host name to test that server. The check reads the greeting, the capabilities, the TLS session and the certificate, and checks the reverse DNS.
How the check works
The MX records are looked up and up to 5 servers are contacted in parallel, on port 25, over IPv4.
Each session is: read the banner, EHLO, STARTTLS, EHLO again inside TLS, QUIT. Each step has 5 seconds.
The certificate is checked separately from the handshake, so an expired, untrusted or wrongly named certificate is shown instead of ending the test.
The server's IP address is looked up in reverse DNS, and the name found is resolved again to confirm it (FCrDNS).
Good to know
- Where the test comes from
Connections come from
probe.exim.ro (91.239.230.137). - Nothing is delivered
Only EHLO, STARTTLS and QUIT are sent: no message and no relay test.
- Limits
No MAIL FROM, RCPT TO or DATA is ever sent, so the check never tests or uses a relay. Private, loopback and reserved addresses are never contacted. Each network may run 6 checks a minute.
Background: Testing an SMTP server: banner, STARTTLS, certificate