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SMTP Penetration Testing · zebbern | DecimalAI

securityby zebbern

SMTP Penetration Testing

zebbern/smtp-penetration-testing

Source zebbern/claude-code-guide ↗License MIT

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.

SkillScore91Maintained

Automatic

Security & AppSec pack

Last verified 8/10/2026

What it changes

Passed 20 of 22 test cases with the skill, and 16 of 22 without it.

Without skill73%

With skill91%

Checks it passed that the model alone missed

Specifies smtp-user-enum as the CLI tool.
Sets USER_FILE to specify the input dictionary.
Sets the mode parameter to VRFY via the -M flag.

and 2 more in the full report

4 fixed16 passed either way2 still failing0 broke

Pass-rate lift: +18 pp
Tokens: +217%
Agent turns: 0%
Response time: -14%

Model gemini-3.6-flashMeasured 8/10/2026v120 of 22 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/zebbern-smtp-penetration-testing/SKILL.md https://app.decimal.ai/s/zebbern-smtp-penetration-testing/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add zebbern-smtp-penetration-testing, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/zebbern-smtp-penetration-testing/ and pins it in .decimal/skills.lock

decimalai skills add zebbern-smtp-penetration-testing

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/zebbern-smtp-penetration-testing/SKILL.md https://app.decimal.ai/s/zebbern-smtp-penetration-testing/SKILL.md

Raw file: /s/zebbern-smtp-penetration-testing/SKILL.md ↗ · machine-readable summary at /s/zebbern-smtp-penetration-testing.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 4 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 4

Prompt

When scanning an internal network for SMTP user enumeration using Metasploit, which exact auxiliary module path should be loaded in msfconsole?

What was checked, without and with the skill
Checked	Without skill	With skill
Specifies auxiliary/scanner/smtp/smtp_enum as the Metasploit module path.	Passed	Passed
Sets USER_FILE to specify the input dictionary.	Missed	Passed

case-06 · gemini-3.6-flash · 8/10/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md492 linessingle file

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

Track record

Benchmark

20 / 22

test cases passed, vs 16 / 22 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

zebbern / claude-code-guide

skills/smtp-penetration-testing/SKILL.md

View on GitHub ↗

License MITImported 8/3/2026Version v1

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See it in action

What's inside

SMTP Penetration Testing

Purpose

Prerequisites

Required Tools

Required Knowledge

Required Access

Outputs and Deliverables

Track record

Benchmark

Adoption

SkillSafety

Source

Other skills for the same job

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