MAIL-04 / DIAGNOSTICS
SMTP Banner Check
Connect to a mail server and read the greeting banner it sends, plus the capabilities it advertises in response to EHLO.
About the SMTP Banner
The SMTP banner is the first line a mail server sends when you connect — it identifies the server and, after an EHLO, lists the features it supports. This tool connects to a mail server and shows its banner and advertised capabilities.
What this tool checks
It connects on the chosen port, reads the greeting banner, sends EHLO, and lists the capabilities the server advertises, such as STARTTLS, SIZE, and AUTH methods.
Why inspect the banner
The banner and capability list reveal whether a server supports encryption, its software and version, and its configuration — useful for diagnosing delivery and security issues.
Frequently asked questions
What is an SMTP banner?
It's the greeting line a mail server sends immediately on connection, usually starting with code 220, identifying the server. After EHLO it also lists supported capabilities.
Which SMTP port should I check?
Port 25 for server-to-server mail, 587 for authenticated submission, and 465 for implicit TLS. Check the port relevant to how you connect to the server.
What can the banner tell me?
It reveals the server software, whether STARTTLS is offered, accepted authentication methods, message size limits, and other capabilities that affect deliverability.