Test SMTP connectivity to a mail server, verify the banner and EHLO handshake
• Server address：Enter the mail server hostname or IP (e.g. mail.example.com)
• Port selection：25 = standard SMTP, 587 = submission (recommended), 465 = SMTPS
• What is checked：TCP connection, 220 banner read, EHLO handshake response
• Node selection：Optionally select specific nodes; all available nodes are used by default
An SMTP test establishes a TCP connection to a mail server on the selected port (25, 587, or 465), reads the 220 greeting banner, and performs an EHLO handshake to verify that the server responds correctly. This confirms that the port is reachable, the service is running, and the server identifies itself as expected.
Common uses include verifying that a newly deployed mail server is accessible from external networks, diagnosing email delivery failures caused by unreachable or misconfigured SMTP servers, confirming which TLS modes are advertised in the EHLO response, and checking that firewall or security group rules allow inbound SMTP traffic on the correct port.
Port 25 is the standard SMTP relay port used for server-to-server delivery. Port 587 (STARTTLS submission) is the recommended port for client-to-server authenticated submission. Port 465 (SMTPS) uses implicit TLS and is still used by some providers.
A passing SMTP test only confirms TCP reachability and the basic banner/EHLO handshake. Delivery failures can also be caused by authentication failures, TLS negotiation problems, spam filtering, blacklisting, or SPF/DKIM/DMARC rejections.
The EHLO response lists the extensions the server supports, including STARTTLS, AUTH mechanisms, SIZE limits, and PIPELINING. This tells you what capabilities the server advertises and whether TLS is available.
Many ISPs and cloud providers block outbound port 25 by default to prevent spam. Use port 587 for client submission. For server-to-server testing, you may need a probe node on a network that allows outbound port 25.