MultiSMTP Validator

Advanced multi-threaded SMTP server credential validation tool with real send-test verification.

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LEGAL NOTICE: This tool is intended exclusively for authorized security research, SMTP server auditing on systems you own, or penetration testing with explicit written permission. Unauthorized use is illegal. The authors assume no responsibility for misuse.

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Features

• Multi-threaded processing — parallel validation scaled to available CPU cores
• Real send-test validation — verifies SMTP credentials by attempting an actual authentication and send
• TCP pre-check — fast port connectivity test before attempting full SMTP handshake
• Result categorization — separates results into valid, invalid, reject, and fail
• Custom input format — supports smtp://host:user:password URL format
• Colorful console UI — clear status output with emoji indicators
• Auto-save results — writes categorized results to Results/ directory

Requirements

Requirement	Version
Windows	10 / 11 (x64)
Pre-compiled binary	No Node.js required
Node.js (source only)	18+

Installation

Option 1: Pre-compiled Binary (Recommended)

1. Download multi-smtp.exe from Releases
2. Place it in any folder
3. Run multi-smtp.exe

Option 2: From Source

git clone https://github.com/ByteCodeSecure/MultiSMTP.git
cd MultiSMTP
npm install
node main.js

Build from Source

# Windows
build.bat

Or manually:

npm install -g pkg
pkg . --out-path=build --targets node18-win-x64

Usage

Run the executable and provide the required information:

multi-smtp.exe

You will be prompted for:

1. SMTP list file path — path to your file containing SMTP servers
2. Test email address — a valid email where validation messages will be sent

Input Format

The SMTP list file must contain one server per line using the following URL format:

smtp://mail.example.com:587:user@example.com:password
smtp://smtp.provider.net:465:admin@provider.net:secretpass
smtps://secure.mail.com:465:user@secure.mail.com:mypassword

Format: smtp[s]://host:port:username:password

• smtp:// — standard SMTP
• smtps:// — SMTP with SSL
• host — SMTP server hostname
• port — SMTP port (common: 25, 465, 587)
• username — authentication username (usually the email address)
• password — authentication password

Output Files

All results are saved in the Results/ directory:

File	Contents	Status
Results/valid.txt	Successfully authenticated and sent	✅ Valid
Results/invalid.txt	Authentication failed	❌ Invalid
Results/reject.txt	Connection accepted but send rejected	🚫 Reject
Results/fail.txt	Could not connect to server	⚠️ Fail

Status Definitions

Status	Meaning
valid	TCP connection succeeded + SMTP auth succeeded + test email sent
invalid	Connected but authentication failed (wrong credentials)
reject	Connected and authenticated but message was rejected
fail	Could not establish TCP connection to the server

Project Structure

MultiSMTP/
├── core/
│   └── checker.js          # Main SMTP verification orchestrator
├── models/
│   └── smtp.js             # Data models (SmtpServer, SmtpResult)
├── services/
│   └── smtp_service.js     # SMTP validation logic (nodemailer + tcp)
├── build/                  # Compiled binaries
├── main.js                 # Application entry point
├── package.json
└── build.bat               # Windows build script

Technical Details

Validation Process

1. TCP Check — Opens a raw TCP socket to host:port with a 5-second timeout
2. SMTP Auth — Uses nodemailer to authenticate with provided credentials
3. Send Test — Attempts to send a real email to the provided test address
4. Result — Classifies the outcome as valid / invalid / reject / fail

Concurrency

MultiSMTP automatically determines the thread count based on available CPU cores:

maxConcurrent = Math.max(2, Math.floor(os.cpus().length / 2))

TLS Configuration

• Port 465 → secure: true (SSL/TLS)
• Other ports → secure: false (STARTTLS or plain)
• Self-signed certificates are accepted (rejectUnauthorized: false)

License

This project is licensed under the MIT License — see LICENSE for full details.

USE RESPONSIBLY. FOR AUTHORIZED USE ONLY.

Contributing

Pull requests are welcome. For major changes, please open an issue first.

Author

ByteCodeSecure — GitHub