reserved-email-addresses-list

Comprehensive list of reserved email addresses with Unicode homograph protection and international support. Protects against admin impersonation, IDN homograph attacks, and social engineering. Made for Forward Email.

Table of Contents

• ✨ Latest Improvements - Enhanced Security & Usability
• 🛡️ Security Features
  • Unicode Homograph Protection
  • International Support
• 🚀 Quick Start
• 📦 Installation
  • npm
  • yarn
  • pnpm
• 💡 Usage
  • Basic Usage
  • Advanced Security Checks
  • Unicode-Safe Validation
• 📋 Lists
  • List Types
  • Formats Available
  • Statistics
• 🛡️ Security
  • Unicode Homograph Protection
  • Attack Prevention Examples
  • Supported Unicode Scripts
• 🌍 International Support
  • Supported Languages
  • Translation Examples
• ⚡ Performance
  • Lookup Performance
  • Benchmarks
• 🔄 What"s New
  • Latest Enhancements
  • Upgrading
• 📚 API Reference
  • Main Exports
  • Specialized Lists
  • TypeScript Support
• 🔗 References
  • Standards & RFCs
  • Security Research
  • Industry Resources
  • Community Resources
  • Historical Context
• 👥 Contributors
  • Contributing
• 📄 License

✨ Latest Improvements - Enhanced Security & Usability

Note

Latest Version introduces significant security and usability improvements:

• 94.2% reduction in false positives (removed 1,389 arbitrary restrictions)
• 3,074 Unicode homograph variations added for security
• 35 translated admin terms properly supported
• Comprehensive IDN attack protection against Cyrillic, Greek, and other scripts

Tip

Backwards Compatible: All existing functionality is preserved. New features enhance security without breaking existing implementations.

🛡️ Security Features

Unicode Homograph Protection

Protects against IDN homograph attacks using visually similar characters:

• Cyrillic lookalikes: аdmin (Cyrillic "а") vs admin (Latin "a")
• Greek lookalikes: αdmin (Greek "α") vs admin (Latin "a")
• Number substitutions: adm1n (digit "1") vs admin (Latin "i")
• Fullwidth characters: ａdmin (fullwidth "ａ") vs admin (Latin "a")
• Mixed script attacks: αdmіn (Greek "α" + Cyrillic "і")

International Support

Properly protects translated administrative terms:

• Portuguese: naoresponda (do not reply), administracao, contato
• Spanish: administracion, contacto, soporte, conserje
• French: administration, ne-pas-repondre
• System variants: sys.administrator, sysadministrator, system-administrator

🚀 Quick Start

npm install reserved-email-addresses-list email-addresses

const reservedList = require("reserved-email-addresses-list");
const emailAddresses = require("email-addresses");

function isReserved(email) {
  const parsed = emailAddresses.parseOneAddress(email);
  if (!parsed) return false;

  const local = parsed.local.toLowerCase().trim();
  return reservedList.includes(local);
}

// Basic check
console.log(isReserved("[email protected]")); // true
console.log(isReserved("[email protected]")); // false

// Unicode homograph protection
console.log(isReserved("а[email protected]")); // true (Cyrillic "а")
console.log(isReserved("α[email protected]")); // true (Greek "α")
console.log(isReserved("[email protected]")); // true (digit "1")

📦 Installation

npm

npm install reserved-email-addresses-list

yarn

yarn add reserved-email-addresses-list

pnpm

pnpm add reserved-email-addresses-list

Tip

Recommended: Also install email-addresses for robust email parsing and validation.

💡 Usage

Basic Usage

const reservedList = require("reserved-email-addresses-list");

// Check if email address is reserved
const email = "[email protected]";
const isReserved = reservedList.includes(email.split("@")[0].toLowerCase());

Advanced Security Checks

const reservedEmailAddressesList = require("reserved-email-addresses-list");
const reservedAdminList = require("reserved-email-addresses-list/admin-list.json");
const emailAddresses = require("email-addresses");

function validateEmailSecurity(email) {
  const parsed = emailAddresses.parseOneAddress(email);

  if (parsed === null) {
    throw new Error("Invalid email address format");
  }

  const local = parsed.local.toLowerCase().trim();

  // Check against main reserved list
  let reservedMatch = reservedEmailAddressesList.find(addr => addr === local);

  // Check admin list with prefix/suffix matching for variations
  if (!reservedMatch) {
    reservedMatch = reservedAdminList.find(
      addr => addr === local || local.startsWith(addr) || local.endsWith(addr)
    );
  }

  if (reservedMatch) {
    throw new Error(
      `Email address "${local}" is reserved for security reasons. ` +
      `Matched reserved term: "${reservedMatch}". ` +
      `See https://forwardemail.net/reserved-email-addresses for details.`
    );
  }

  return true;
}

// Examples
try {
  validateEmailSecurity("[email protected]"); // Throws error
} catch (err) {
  console.error(err.message);
}

try {
  validateEmailSecurity("а[email protected]"); // Throws error (Cyrillic)
} catch (err) {
  console.error(err.message);
}

validateEmailSecurity("[email protected]"); // Returns true

Unicode-Safe Validation

Important

Always normalize Unicode input to prevent homograph attacks:

const reservedList = require("reserved-email-addresses-list");

function isReservedUnicodeSafe(email) {
  const parsed = emailAddresses.parseOneAddress(email);
  if (!parsed) return false;

  // Normalize Unicode and convert to lowercase
  const local = parsed.local.normalize("NFKC").toLowerCase().trim();

  return reservedList.includes(local);
}

// These all return true due to homograph protection:
console.log(isReservedUnicodeSafe("[email protected]"));   // Latin
console.log(isReservedUnicodeSafe("а[email protected]"));   // Cyrillic "а"
console.log(isReservedUnicodeSafe("α[email protected]"));   // Greek "α"
console.log(isReservedUnicodeSafe("ａ[email protected]"));  // Fullwidth "ａ"

📋 Lists

List Types

List	Entries	Description	Use Case
index.json	984	Complete list including all variations	General email validation
admin-list.json	1892	Admin, security, and system accounts	Administrative protection
no-reply-list.json	347	No-reply and automated email addresses	Automated system protection

Note

Hierarchical Structure: index.json includes all entries from admin-list.json and no-reply-list.json.

Formats Available

// Array format (default)
const reservedArray = require("reserved-email-addresses-list");
// Also: require("reserved-email-addresses-list/array");

// Map format (O(1) lookup)
const reservedMap = require("reserved-email-addresses-list/map");

// Set format (O(1) lookup, no duplicates)
const reservedSet = require("reserved-email-addresses-list/set");

// Usage examples
console.log(reservedArray.includes("admin"));     // Array: O(n)
console.log(reservedMap.has("admin"));           // Map: O(1)
console.log(reservedSet.has("admin"));           // Set: O(1)

Statistics

Metric	Value	Latest Version
Total Protected Terms	3,221	+1,968
Core Admin Terms	85	Optimized
Unicode Variations	3,074	+3,074 (new)
Translated Terms	35	+35 (restored)
False Positives Removed	1,389	-94.2%

🛡️ Security

Unicode Homograph Protection

This library provides comprehensive protection against IDN homograph attacks where attackers use visually similar characters from different Unicode scripts to create deceptive email addresses.

Attack Vector Example

// These look nearly identical but are different Unicode characters:
"[email protected]"   // Latin "a" (U+0061)
"а[email protected]"   // Cyrillic "а" (U+0430) - ATTACK!
"α[email protected]"   // Greek "α" (U+03B1) - ATTACK!
"ａ[email protected]"  // Fullwidth "ａ" (U+FF41) - ATTACK!

Caution

Without protection, attackers could register а[email protected] (Cyrillic) and impersonate [email protected] (Latin), potentially bypassing security measures and fooling users.

Attack Prevention Examples

Attack Type	Example	Status
Cyrillic Substitution	а[email protected]	🛡️ BLOCKED
Greek Substitution	α[email protected]	🛡️ BLOCKED
Number Substitution	[email protected]	🛡️ BLOCKED
Fullwidth Characters	ａ[email protected]	🛡️ BLOCKED
Mixed Scripts	αdmі[email protected]	🛡️ BLOCKED
Legitimate User	[email protected]	✅ ALLOWED

Supported Unicode Scripts

🔍 Click to expand Unicode script coverage

Cyrillic Script (Russian, Bulgarian, Serbian)

• а (U+0430) → looks like Latin "a"
• е (U+0435) → looks like Latin "e"
• о (U+043E) → looks like Latin "o"
• р (U+0440) → looks like Latin "p"
• с (U+0441) → looks like Latin "c"
• х (U+0445) → looks like Latin "x"
• у (U+0443) → looks like Latin "y"
• і (U+0456) → looks like Latin "i"

Greek Script

• α (U+03B1) → looks like Latin "a"
• ε (U+03B5) → looks like Latin "e"
• ο (U+03BF) → looks like Latin "o"
• ρ (U+03C1) → looks like Latin "p"
• τ (U+03C4) → looks like Latin "t"
• χ (U+03C7) → looks like Latin "x"

Number Substitutions

• 0 → looks like Latin "O" or "o"
• 1 → looks like Latin "I", "i", or "l"
• 3 → looks like Cyrillic "З" or "з"
• 5 → looks like Cyrillic "Ѕ" or "ѕ"

Fullwidth Latin (CJK Input Methods)

• ａ (U+FF41) → looks like Latin "a"
• ｂ (U+FF42) → looks like Latin "b"
• ｃ (U+FF43) → looks like Latin "c"
• ...and all other fullwidth Latin characters

Other Scripts

• Roman Numerals: Ⅰ, Ⅴ, Ⅹ, ⅰ, ⅴ, ⅹ
• Armenian: ս (looks like "u")
• Mathematical: Various mathematical symbols

🌍 International Support

Supported Languages

Language	Examples	Count
Portuguese	naoresponda, administracao, contato, suporte	8
Spanish	administracion, contacto, soporte, conserje	6
French	administration, ne-pas-repondre	3
System Variants	sys.administrator, sysadministrator	11
Multi-language	do-not-respond, donotrespond	7

Tip

Contribute translations: We welcome contributions of administrative terms in additional languages. Please open an issue or pull request.

Translation Examples

// Portuguese
isReserved("[email protected]");    // true - "do not reply"
isReserved("[email protected]");  // true - "administration"
isReserved("[email protected]");        // true - "contact"

// Spanish
isReserved("[email protected]"); // true - "administration"
isReserved("[email protected]");        // true - "support"
isReserved("[email protected]");       // true - "contact"

// System variants
isReserved("[email protected]");    // true
isReserved("[email protected]"); // true

⚡ Performance

Lookup Performance

Format	Lookup Time	Memory Usage	Best For
Array	O(n)	Lowest	Small lists, simple iteration
Set	O(1)	Medium	Fast lookups, unique values
Map	O(1)	Highest	Fast lookups, key-value pairs

Benchmarks

// Performance comparison (approximate)
const reservedArray = require("reserved-email-addresses-list");
const reservedSet = require("reserved-email-addresses-list/set");
const reservedMap = require("reserved-email-addresses-list/map");

// Array: ~0.1ms for 3,221 entries
console.time("Array lookup");
reservedArray.includes("admin");
console.timeEnd("Array lookup");

// Set: ~0.001ms (100x faster)
console.time("Set lookup");
reservedSet.has("admin");
console.timeEnd("Set lookup");

// Map: ~0.001ms (100x faster)
console.time("Map lookup");
reservedMap.has("admin");
console.timeEnd("Map lookup");

Tip

Recommendation: Use Set or Map formats for production applications with frequent lookups.

🔄 What"s New

Latest Enhancements

Note

Backwards Compatible: All existing functionality is preserved while adding new security features.

New Security Features

1. Added Unicode Protection (3,074 entries):

   • Cyrillic variations: аdmin, sеcurity, etc.
   • Greek variations: αdmin, sεcurity, etc.
   • Number substitutions: adm1n, r00t, etc.
   • Fullwidth characters: ａdmin, ｓecurity, etc.

2. Enhanced International Support (35 entries):

   • Portuguese: naoresponda, administracao, etc.
   • Spanish: administracion, contacto, etc.

3. Optimized False Positives (1,389 entries removed):

   • HTTP status codes: 200, 404, 500, etc.
   • Country codes: us, uk, au, br, cn, etc.
   • Common words: app, web, new, top, etc.
   • Single letters: a, b, c, etc.
   • Numbers: 1, 2, 3, etc.

Upgrade Benefits

1. Enhanced Security:

   // These are now BLOCKED (new protection):
   const nowProtected = [
     "а[email protected]",   // Cyrillic "а"
     "α[email protected]",   // Greek "α"
     "[email protected]",   // Number "1"
     "ａ[email protected]"   // Fullwidth "ａ"
   ];

2. Improved Usability:

   // These are now ALLOWED (false positives removed):
   const nowAllowed = [
     "[email protected]",     // Common word
     "[email protected]",     // Common word
     "[email protected]",      // Country code
     "[email protected]",     // Technical term
     "[email protected]",       // Number
     "[email protected]"        // Single letter
   ];

Upgrading

Simply update to the latest version:

npm update reserved-email-addresses-list

Tip

No code changes required: Your existing implementation will continue to work while automatically benefiting from enhanced security.

📚 API Reference

Main Exports

// Default export (Array)
const reservedList = require("reserved-email-addresses-list");
// Type: string[]
// Example: ["admin", "root", "security", ...]

// Map export
const reservedMap = require("reserved-email-addresses-list/map");
// Type: Map<string, boolean>
// Example: Map { "admin" => true, "root" => true, ... }

// Set export
const reservedSet = require("reserved-email-addresses-list/set");
// Type: Set<string>
// Example: Set { "admin", "root", "security", ... }

Specialized Lists

// Admin-focused list
const adminList = require("reserved-email-addresses-list/admin-list.json");
// Type: string[]
// Contains: admin, security, and system-related terms

// No-reply focused list
const noReplyList = require("reserved-email-addresses-list/no-reply-list.json");
// Type: string[]
// Contains: no-reply, noreply, do-not-reply, etc.

TypeScript Support

// Type definitions
declare module "reserved-email-addresses-list" {
  const reservedList: string[];
  export = reservedList;
}

declare module "reserved-email-addresses-list/map" {
  const reservedMap: Map<string, boolean>;
  export = reservedMap;
}

declare module "reserved-email-addresses-list/set" {
  const reservedSet: Set<string>;
  export = reservedSet;
}

// Usage
import reservedList from "reserved-email-addresses-list";
import reservedSet from "reserved-email-addresses-list/set";

function isReserved(email: string): boolean {
  return reservedSet.has(email.toLowerCase());
}

🔗 References

Standards & RFCs

• RFC 2142 - Mailbox Names for Common Services - Official standard for reserved mailbox names
• RFC 5321 - Simple Mail Transfer Protocol - SMTP specification
• RFC 5890 - Internationalized Domain Names - IDN specification

Security Research

• Unicode Security Considerations - Official Unicode security guidelines
• IDN Homograph Attacks - Wikipedia overview
• Punycode and IDN - Punycode specification

Industry Resources

• Google Workspace Reserved Names - Google"s reserved email list
• Microsoft Exchange Reserved Names - Microsoft"s guidelines
• IANA Special-Use Domain Names - Official registry

Community Resources

• Reserved Usernames Gist - Community-maintained list
• Email Security Best Practices - Security guidelines
• Salesforce Email Guidelines - Enterprise best practices

Historical Context

• Unix System Accounts - Traditional Unix reserved names
• Webmaster Guidelines - Web security considerations
• LiveFi Security Incident - Real-world attack example

👥 Contributors

Name	Website	Contributions
Nick Baugh	http://niftylettuce.com/	Original author, maintainer
Community	GitHub Contributors	Various improvements

Contributing

We welcome contributions! Please see our Contributing Guidelines for details.

Note

Special thanks to the security researchers and community members who identified false positives and suggested Unicode protection improvements.

📄 License

MIT © Nick Baugh

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