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Email Tools
Full SMTP conversation, banner, TLS and relay check.
The SMTP Test opens a full SMTP conversation with a mail server, capturing the banner, the supported extensions, whether STARTTLS is offered, and whether the server would accept (relay) a message for an external recipient.
Enter a mail host (mail.example.org) and run the tool. The probe connects on port 25 and walks through the SMTP handshake, reporting each stage.
Input: Mail host — e.g. mail.example.org.
The output shows the server banner, the extensions advertised by EHLO (SIZE, PIPELINING, STARTTLS, AUTH…), whether TLS was negotiated, and the result of a relay test. An "open relay" result is a serious misconfiguration that allows anyone to send mail through your server and will get you blacklisted quickly.
→ Check a mail server banner and EHLO extensions after a change.
→ Confirm STARTTLS is offered on port 25.
→ Verify a server is not an open relay before going live.
→ Diagnose why a remote mail server cannot deliver to yours.
An open relay accepts outbound mail from unauthenticated, arbitrary senders for arbitrary recipients. Spammers abuse it to send bulk mail through your server, which gets your IP blacklisted and your legitimate mail blocked. Always require authentication for submission and restrict relay to authenticated users or trusted IPs.
Yes. STARTTLS upgrades a plain SMTP connection to TLS opportunistically. While it is not a substitute for MTA-STS/DANE, offering it improves transport confidentiality and is expected by modern mail providers.
The test connects on port 25 (SMTP), which is used for server-to-server delivery. Submission from email clients uses port 587 (or 465 for implicit TLS) and requires authentication; those ports are not tested here.