SMTP Penetration Testing

To test for an open relay on an SMTP server, you simulate unauthorized email routing attempts to detect misconfigurations that allow external message forwarding. This process identifies server vulnerabilities where access controls are absent.

Enumerating SMTP users via VRFY and EXPN involves sending these protocol commands to verify specific email addresses or expand mailing lists. This technique exposes valid internal accounts and distribution group memberships on the target mail server.

Performing brute-force authentication testing on SMTP requires automated tools to systematically guess credentials. This validates the strength of password policies and identifies weak login mechanisms protecting the mail infrastructure.

Checking TLS configuration and validating SSL certificates on a mail server requires inspecting the cryptographic handshake and certificate chain. This identifies weak protocol versions, expired certificates, and insecure encryption algorithms.

Analyzing SPF, DKIM, and DMARC records involves querying DNS-based authentication configurations to prevent email spoofing. This assessment verifies domain alignment and provides remediation guidance to harden email security posture.

Baseline tools required for SMTP penetration testing include Nmap for service discovery, smtp-user-enum for account harvesting, and Hydra for credential attacks. These tools facilitate comprehensive security assessments across common mail infrastructures.