EHLO Checker

The EHLO Checker analyzes SMTP servers by performing a standards-based EHLO handshake to expose the server’s advertised features and security posture. It is designed for developers, DevOps, and security engineers who implement or troubleshoot mail infrastructure. It focuses on protocol behavior, capability discovery, and pass/fail indicators relevant to deliverability and policy alignment.

Conceptually, the tool connects to a target host and port, negotiates TLS if requested, sends an EHLO with a client hostname, and collects the server’s 250 responses. It parses tokens such as STARTTLS, AUTH methods, SIZE, 8BITMIME, PIPELINING, SMTPUTF8, and ENHANCEDSTATUSCODES, then returns a structured report for automation.

Value and differentiators include automated TLS verification, explicit capability listing, cross-version checks (IPv4/IPv6), and machine-readable output suitable for CI pipelines. It does not perform mail sending or relay tests, aligning with safe diagnostic use and RFC-compliant behavior.

Core features cover single-shot checks and batch analyses, configurable timeouts, and a standardized schema for results. Use cases include deliverability troubleshooting, policy verification, relay restriction assessment, and baseline validation during server migrations or domain onboarding.