SMTP Server Tester
Connect to a domain's real mail server and run a live SMTP handshake: banner, EHLO capabilities and STARTTLS. Free SMTP tester over a genuine connection.
Test an SMTP server
Enter a domain to test its receiving mail server (MX, port 25), or a submission host like smtp.gmail.com to test port 587/465.
A domain resolves to its MX record, which accepts mail on port 25. Submission ports (587/465) are served by a separate host — enter that host directly (e.g. smtp.gmail.com).
What this SMTP tester does
Common use cases
- 1Verifying a mail server accepts connections
- 2Checking a server offers TLS encryption
- 3Confirming SMTP setup after DNS changes
- 4Debugging why mail is being rejected
- 5Auditing a provider's SMTP capabilities
- 6Testing a submission port before configuring a client
Related tools
About SMTP servers
SMTP (Simple Mail Transfer Protocol) is how mail servers accept and relay email. A healthy server answers with a banner, advertises its capabilities in response to EHLO, and offers STARTTLS so the conversation can be encrypted.
This tool resolves the domain's MX record, connects to the real server and runs that handshake live. Note that port 25 is frequently blocked for outbound connections (including on many cloud hosts), so use 587 or 465 for the most reliable results — the tool tells you honestly when a connection cannot be made.
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Got Questions? We Have Answers.
What does the SMTP server tester check?
It resolves the domain's MX record, opens a real SMTP connection to that server, reads the greeting banner, lists the EHLO capabilities and checks whether STARTTLS encryption is offered.
Which port should I use?
Use 587 (submission) or 465 (SMTPS) for reliable results. Port 25 is widely blocked for outbound connections, so tests against it often fail even when the server is healthy.
Why does the connection fail on port 25?
Most networks and cloud hosts block outbound port 25 to curb spam. The tool tells you honestly when this happens — switch to 587 or 465.
What is EHLO?
EHLO is the SMTP greeting a client sends; the server replies with the features it supports, such as STARTTLS, SIZE and AUTH. The tester lists them for you.
Is the test a real connection?
Yes. It opens a genuine TCP/SMTP conversation with the mail server at the moment you run it — no cached or sample data.
Why does it use the MX record?
The MX record names the server that accepts mail for a domain, so testing it checks the host that actually receives your email.