Open Skills Logo
Open Skills

SMTP Penetration Testing

This skill should be used when the user asks to "perform SMTP penetration testing", "enumerate email users", "test for open mail relays", "grab SMTP banners", "brute force email credentials", or "assess mail server security". It provides comprehensive techniques for testing SMTP server security.

Author

zebbern

Category

Other Tools

Install

Hot:9

Download and extract to your skills directory

Copy command and send to OpenClaw for auto-install:

Download and install this skill https://openskills.cc/api/download?slug=sickn33-skills-smtp-penetration-testing&locale=en&source=copy

SMTP Penetration Testing Skills

Skill Overview


SMTP Penetration Testing is a professional email server security assessment skill used to detect SMTP service vulnerabilities, perform user enumeration, test for open relays, and generate security hardening recommendations within an authorized scope.

Suitable Scenarios

1. Corporate Email System Security Assessment


With prior written authorization, conduct comprehensive security testing of an organization’s internal or externally available mail servers to identify common issues such as open relays and weak authentication and user enumeration. Deliver professional security assessment reports and hardening suggestions.

2. CTF Competitions and Security Research


Suitable for CTF challenges related to SMTP services, as well as for security researchers studying and learning about email protocol security. The skill includes a complete reference of SMTP commands, explanations of response codes, and exploitation methods.

3. Email Server Compliance Checks


Helps system administrators and security teams verify whether mail server configurations comply with security best practices, including detecting TLS/SSL settings, analyzing SPF/DKIM/DMARC records, checking for banner information leakage, and more.

Core Functions

1. Comprehensive SMTP Service Discovery


  • Service discovery: Automatically identify SMTP servers and related ports (25/465/587/2525), and parse MX records

  • Banner grabbing: Retrieve server version information, supported extensions, and feature capabilities

  • Command enumeration: Test the availability of commands such as VRFY, EXPN, and RCPT TO

    • 2. Vulnerability and Security Assessment


  • Open relay testing: Determine whether the mail server can be abused to send spam

  • User enumeration: Verify whether email users exist using multiple methods

  • Authentication security testing: Test for weak password credentials and assess brute-force risk

  • Encryption testing: Evaluate STARTTLS/SSL configuration and the security of encryption ciphers

    • 3. Security Hardening Recommendations


    Based on the results, provide targeted hardening recommendations for the mail server, including disabling open relays, disabling dangerous commands, enforcing TLS encryption, configuring SPF/DKIM/DMARC, implementing rate limiting, and more.

    Common Questions

    Is SMTP penetration testing legal?


    SMTP penetration testing must be performed only with prior, explicit written authorization from the system owner. Testing mail servers without authorization is illegal. This skill is intended only for authorized security assessments, compliance checks, CTF competitions, and learning/research scenarios.

    What tools are needed for SMTP testing?


    Common tools include: Nmap (port scanning and script testing), Netcat/Telnet (manual protocol interaction), Hydra (credential brute-forcing), smtp-user-enum (user enumeration), Metasploit (automated exploitation modules), and OpenSSL (TLS/SSL testing). The skill includes detailed usage examples for each tool.

    How to protect an SMTP server from attacks?


    Recommended measures include: disabling open relays and requiring authentication for external delivery; disabling VRFY/EXPN commands to prevent user enumeration; enforcing STARTTLS encryption; configuring SPF/DKIM/DMARC to prevent email spoofing; implementing rate limits for failed logins and account lockout policies; regularly updating mail server software and monitoring security logs.