SMTP Server Test
Connect to a mail server on port 25 and check its greeting, STARTTLS support and TLS certificate, just as a sending server would.
Free, no account needed.
What this check looks at
- Whether the server accepts connections on port 25, and how long it takes to answer.
- The SMTP banner, and whether its hostname matches the server's reverse DNS.
- STARTTLS support, the TLS version, and whether the certificate is valid, trusted and matches the hostname.
- Enter a domain to test its highest-priority MX server.
Why encryption matters
Most mail between servers is now encrypted with STARTTLS. A missing or broken certificate can make some senders fall back to plain text, and with MTA-STS enforced, mail to you may not be delivered at all. Keep the certificate renewed and matching your MX hostnames.
Frequently asked questions
Why does the test time out?
The server may not accept connections from the internet on port 25, a firewall may block it, or the hostname may not have a mail server behind it.
Do you send an email during the test?
No. We open the connection, read the greeting, try STARTTLS and disconnect politely without sending a message.
Related tools
- MX Record LookupSee which mail servers receive email for a domain, in priority order, with their IP addresses and reverse DNS.
- MTA-STS CheckerCheck that MTA-STS is set up correctly, so other mail servers only deliver to you over verified, encrypted connections.
- Email Blacklist CheckCheck an IP address or domain against widely used DNS blocklists, the lists mail servers consult to reject spam.
- Email Domain Health CheckRun every email and DNS check for a domain at once and get a single report with everything that needs attention.