Claude Code Guide is a reference collection for configuring and using Claude Code, Anthropic’s command-line coding agent. Developers use it to learn commands, skills, agents, MCP, automation, security, integrations, and troubleshooting. Its catalogue add-ons provide many of the documented skills and agents.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/zebbern/claude-code-guide/smtp-penetration-testingnpx skills add zebbern/claude-code-guide --skill smtp-penetration-testinggit clone --depth 1 https://github.com/zebbern/claude-code-guideWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/zebbern/claude-code-guide/smtp-penetration-testing)<a href="https://agentmods.dev/skills/zebbern/claude-code-guide/smtp-penetration-testing"><img src="https://agentmods.dev/badge/skills/zebbern/claude-code-guide/smtp-penetration-testing.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00066 | $0.03293 |
| Opus 5 | $0.00033 | $0.01647 |
| Sonnet 5 | $0.00013 | $0.00659 |
| Haiku 4.5 | $0.00007 | $0.00329 |
Grade A, and why
smtp-penetration-testing scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Asks for rootlowPrivilege escalation
A mod that escalates privileges can change anything on the machine, not only the project.
sudo apt-get install nmap Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
How it starts
The opening of the file, as written. The whole thing — 501 lines — stays where its author put it; the contents beside it link to each section on GitHub.
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
# 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
- SMTP Security Assessment Report - Comprehensive vulnerability findings
- User Enumeration Results - Valid email addresses discovered
- Relay Test Results - Open relay status and exploitation potential
- 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:
# 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:
# Using Telnet
telnet TARGET_IP 25
# Response: 220 mail.target.com ESMTP Postfix
# Using Netcat
nc TARGET_IP 25
# Response: 220 mail.target.com ESMTP
# Using Nmap
nmap -sV -p 25 TARGET_IP
# Version detection extracts banner info
# Manual SMTP commands
EHLO test
# Response reveals supported extensions
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- yesterday First seen · 501 lines · 66 tokens per session scan A 1f2a1ca7b95f
smtp-penetration-testing is a skill published in the GitHub repository zebbern/claude-code-guide (4,600 stars, last pushed yesterday), licensed MIT. It adds 66 tokens to every session and 3,293 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 1 finding (asks for root). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
Other skills, from other repositories
business-investment-advisor
../../../finance/business-investment-advisor/skills/business-investment-advisor/SKILL.md.
a11y-audit
../../../engineering-team/a11y-audit/skills/a11y-audit/SKILL.md.
adversarial-reviewer
../../../engineering-team/skills/adversarial-reviewer/SKILL.md.
agent-memory
../../../engineering/agent-memory/skills/agent-memory/SKILL.md.
agile-product-owner
../../../product-team/agile-product-owner/skills/agile-product-owner/SKILL.md.
app-store-optimization
../../../marketing-skill/skills/app-store-optimization/SKILL.md.