# Smtp Penetration Testing

Should be used when the user asks to "perform SMTP penetration testing", "enumerate...

- Repository: https://github.com/zebbern/claude-code-guide (4691 stars)
- Category: Testing
- License: MIT
- Last updated: 2026-11-01
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add zebbern/claude-code-guide --skill smtp-penetration-testing -g -a claude-code -y`
Codex: `npx skills add zebbern/claude-code-guide --skill smtp-penetration-testing -g -a codex -y`
Cursor: `npx skills add zebbern/claude-code-guide --skill smtp-penetration-testing -g -a cursor -y`
Gemini CLI: `npx skills add zebbern/claude-code-guide --skill smtp-penetration-testing -g -a gemini-cli -y`

## Description

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.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# SMTP Penetration Testing

## Purpose

Conduct comprehensive security assessments of SMTP (Simple Mail Transfer Protocol) servers to identify vulnerabilities including open relays, user enumeration, weak authentication, and misconfiguration. This skill covers banner grabbing, user enumeration techniques, relay testing, brute force attacks, and security hardening recommendations.

## Prerequisites

### Required Tools
```bash
# Nmap with SMTP scripts
sudo apt-get install nmap

# Netcat
sudo apt-get install netcat

# Hydra for brute force
sudo apt-get install hydra

# SMTP user enumeration tool
sudo apt-get install smtp-user-enum

# Metasploit Framework
msfconsole
```

### Required Knowledge
- SMTP protocol fundamentals
- Email architecture (MTA, MDA, MUA)
- DNS and MX records
- Network protocols

### Required Access
- Target SMTP server IP/hostname
- Written authorization for testing
- Wordlists for enumeration and brute force

## Outputs and Deliverables

1. **SMTP Security Assessment Report** - Comprehensive vulnerability findings
2. **User Enumeration Results** - Valid email addresses discovered
3. **Relay Test Results** - Open relay status and exploitation potential
4. **Remediation Recommendations** - Security hardening guidance

## Core Workflow

### Phase 1: SMTP Architecture Understanding

```
Components: MTA (transfer) → MDA (delivery) → MUA (client)

Ports: 25 (SMTP), 465 (SMTPS), 587 (submission), 2525 (alternative)

Workflow: Sender MUA → Sender MTA → DNS/MX → Recipient MTA → MDA → Recipient MUA
```

### Phase 2: SMTP Service Discovery

Identify SMTP servers and versions:

```bash
# Discover SMTP ports
nmap -p 25,465,587,2525 -sV TARGET_IP

# Aggressive service detection
nmap -sV -sC -p 25 TARGET_IP

# SMTP-specific scripts
nmap --script=smtp-* -p 25 TARGET_IP

# Discover MX records for domain
dig MX target.com
nslookup -type=mx target.com
host -t mx target.com
```

### Phase 3: Banner Grabbing

Retrieve SMTP server information:

The rest: https://github.com/zebbern/claude-code-guide/blob/HEAD/skills/smtp-penetration-testing/SKILL.md