Test a domain's mail server on port 25: greeting, EHLO features and STARTTLS certificate
Checked from our server in India. Only the address you type is sent to us; nothing else leaves your device. Updated on 18 Oct 2026.An SMTP test connects to a domain's mail server the way another mail server would. This one looks up the MX records, connects to the first server on port 25 from our server in India, reads the 220 greeting and the EHLO features, and checks STARTTLS and its certificate. It sends no email.
Type the mail domain, the part after @ in an email address.
Press Test mail server. Our server looks up the MX records and connects on port 25.
Read the greeting, the features and the STARTTLS verdict, then copy the result.
When someone sends mail to your domain, their server looks up its MX records, connects to the mail server with the highest priority on port 25, and waits for a greeting that starts with 220. It then introduces itself with EHLO, reads the list of features the server supports, and, if STARTTLS is among them, upgrades the connection to TLS before sending anything. The SMTP Test does those same steps from our server and stops there, with QUIT.
The result shows the MX records in priority order, the server tested and its address, how long the connection took, the greeting, and every feature from the EHLO reply, such as SIZE (the largest message accepted), PIPELINING and 8BITMIME. If STARTTLS is offered, the page reports the TLS version and whether the certificate is trusted, names the mail server, and how many days it has left. MTA-STS policies need all three to be right.
No MAIL FROM, no RCPT TO and no message are sent, so no email is delivered and the test cannot be used to check whether an address exists. It is not an open-relay test either.
Many hosting providers block outgoing connections on port 25 to stop spam from their machines, and home internet providers often do the same. If your mail server does not answer, our server also tries Gmail's inbound server once an hour. When that fails too, the block is on our side, and the page says so instead of blaming your server. Domains with a null MX record, which accept no mail at all, are reported as such. Only mail servers on public addresses are tested.
No. Our server reads the greeting, sends EHLO, tries STARTTLS when offered and then sends QUIT. No MAIL FROM, RCPT TO or message is ever sent, so nothing is delivered, no address is checked for existence, and the test is not an open-relay test.
Hosting providers commonly block outgoing port 25 to stop spam. When your mail server does not answer, our server also tries Gmail's inbound server; if that fails too, the block is ours, and the result says nothing about your server. Test from a network that allows outgoing port 25 instead.
STARTTLS is the SMTP command that upgrades a plain connection on port 25 to an encrypted TLS connection. Mail servers use it to protect messages between each other. A server that does not offer it receives mail in clear text, which the test reports as a failure.
The one with the lowest MX priority number, which senders try first. Every MX record is listed so the others can be checked by typing their names. A domain with no MX record is tested at its own address, as the mail standard says, and is flagged.
A null MX is a single MX record with priority 0 and a target of a single dot, defined in RFC 7505. It states that the domain never accepts email, so senders fail at once instead of retrying for days. The test reports it and stops.
Not here: the SMTP test checks port 25, where mail arrives from other servers. Port 465 uses TLS from the first byte, so the SSL Checker reads its certificate when you set the port to 465. Port 587 needs a login and is not tested.
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Also works as: STARTTLS Checker.
Same job, other tools: NS Lookup – Find the name servers a domain is delegated to, and how long resolvers cache them · SRV Record Lookup – Look up SRV records: priority, weight, port and target for a service.