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Validate RFC 5321 compliance of your MTA greeting banner. Analyze FQDN alignment, detect version leakage, and mitigate footprinting vulnerabilities across all your SMTP endpoints.
An SMTP banner is the initial 220 response transmitted by a Mail Transfer Agent (MTA) upon establishing a TCP connection (port 25, 465, or 587). Per RFC 5321, it must contain the server's FQDN to ensure FCrDNS alignment. Default banners often inadvertently leak software versions and OS telemetry, which threat actors exploit for banner grabbing and CVE targeting.
A misconfigured or verbose banner causes FCrDNS failures, increases SpamAssassin scores, triggers 554 rejections, and exposes your server fingerprint to automated vulnerability scanners.
Exposing MTA software versions, using a non-FQDN hostname, and having PTR mismatches are the top banner misconfigurations that degrade deliverability and invite targeted attacks.
Type your domain or mail server hostname into the checker above.
Our engine opens a real TCP connection to port 25 and captures the 220 banner.
Inspect FQDN alignment, PTR match, version exposure, and response latency.
Follow our recommendations to minimize banner exposure and pass FCrDNS checks.
Ensures your MTA's initial 220 response strictly adheres to RFC 5321 specifications, validating the presence of a syntactically correct FQDN to prevent immediate connection drops by rigorous receiving MTAs.
Cross-references the hostname presented in the SMTP banner against reverse DNS (PTR) records to confirm Forward Confirmed reverse DNS alignment, a critical heuristic used by anti-spam filters globally.
Identifies and highlights unnecessary software versioning, OS telemetry, and architectural data exposed in the banner string, allowing you to truncate the response to mitigate reconnaissance and CVE targeting.
Measures the initial TCP handshake and Time-To-First-Byte (TTFB) of the SMTP banner response. Identifies tarpitting configurations or severe latency that could cause client timeouts during the initial SMTP phase.
Executes SMTP banner retrieval across port 25, implicit TLS port 465, and message submission port 587 to ensure consistent identity presentation and protocol compliance across all inbound vectors.
Transitions from the banner to parsing the EHLO response, mapping supported ESMTP extensions (e.g., STARTTLS, 8BITMIME, PIPELINING) to evaluate cryptographic and transport capabilities in one pass.
Automate SMTP banner monitoring, get instant alerts on FCrDNS failures, and receive AI-powered remediation for banner misconfiguration across all your mail servers.