EmailGuard

Zero-dependency, offline email validation for .NET.

EmailGuard validates email addresses through a fast three-step pipeline — no network calls, no external dependencies.

Features

Step	What it does	Speed
1. Quick Guard	Compiled regex rejects obvious junk (missing @, spaces, no domain dot)	⚡ ~nanoseconds
2. RFC Validation	Enforces RFC 5321/5322 rules: atext chars, dot positions, length limits	⚡ ~microseconds
3. TLD Check	Verifies the domain's TLD against a static IANA root zone list	⚡ ~microseconds

Highlights

• 🚫 Zero dependencies — pure .NET, nothing to install
• 🔌 Fully offline — no DNS lookups, no HTTP calls
• 🎯 Multi-target — supports net8.0, net9.0, net10.0
• 📋 Detailed results — tells you which step failed, not just pass/fail
• ⚡ Fast — source-generated regex, Span<T>-based parsing, HashSet<T> TLD lookup

Installation

dotnet add package EmailGuard

Quick Start

using EmailGuard;

// Simple boolean check
if (EmailValidator.IsValid("user@example.com"))
    Console.WriteLine("Valid!");

// Detailed result
var result = EmailValidator.Validate("user@example.com");
switch (result)
{
    case EmailValidationResult.Valid:
        Console.WriteLine("✅ Valid email address.");
        break;
    case EmailValidationResult.InvalidFormat:
        Console.WriteLine("❌ Bad format.");
        break;
    case EmailValidationResult.RfcViolation:
        Console.WriteLine("❌ RFC 5321/5322 violation.");
        break;
    case EmailValidationResult.InvalidTld:
        Console.WriteLine("❌ Unknown TLD.");
        break;
}

API Reference

EmailValidator.Validate(string? email)

Returns an EmailValidationResult enum:

Value	Meaning
Valid	Passed all three validation steps
InvalidFormat	Failed the quick regex guard (step 1)
RfcViolation	Failed RFC 5321/5322 structural checks (step 2)
InvalidTld	Domain TLD not found in the IANA list (step 3)

EmailValidator.IsValid(string? email)

Returns true if the email passes all validation steps; false otherwise.

TldValidator.IsValidTld(string domain)

Returns true if the domain's TLD is in the known IANA list.

RFC Rules Enforced (Step 2)

• Exactly one @ separating local-part and domain
• Total address length ≤ 254 characters
• Local-part length ≤ 64 characters
• Local-part: only RFC 5322 atext characters + dots; no leading, trailing, or consecutive dots
• Domain labels: 1–63 characters each, alphanumeric + hyphens, no leading/trailing hyphens
• At least two domain labels (e.g., example.com)

TLD List (Step 3)

The TLD list is sourced from the IANA Root Zone Database and is embedded as a static HashSet<string>. It includes all country-code, generic, and internationalized (punycode xn--) TLDs.

Last updated: 2026-02-24

To update, replace the list in TldValidator.cs and bump the version.

Project Structure

EmailGuard/
├── src/
│   └── EmailGuard/            # The NuGet package library
├── tests/
│   └── EmailGuard.Tests/      # xUnit unit + smoke tests
├── samples/
│   └── EmailGuard.Sample/     # Console demo app
├── EmailGuard.sln
├── README.md
└── LICENSE

License

MIT