MailJudge

Fastest email validation for Java — without regular expressions

MailJudge provides reliable email validation using character-by-character parsing instead of regular expressions. This approach focuses on predictable performance, clear logic, and easy extensibility.

Features

• Performance-focused validation using direct character parsing
• RFC 5321 checks where applicable
• Predefined rulesets and support for custom rules
• Lightweight with minimal dependencies
• Extensible: add custom validation rules easily

Quick start

Simple usage

import dev.nightowl.mailjudge.MailJudge;
import dev.nightowl.mailjudge.ValidationResult;

// Validate an email with the standard ruleset
ValidationResult result = MailJudge.verify("user@example.com");

if (result.isValid()) {
    System.out.println("Valid email");
} else {
    System.out.println("Invalid: " + result.getErrors());
}

Custom rulesets

import dev.nightowl.mailjudge.MailJudge;
import dev.nightowl.mailjudge.rules.Rulesets;

// Use predefined rulesets
MailJudge standardJudge = MailJudge.withRuleset(Rulesets.standard());
MailJudge strictJudge = MailJudge.withRuleset(Rulesets.strict());
MailJudge noDisposableJudge = MailJudge.withRuleset(Rulesets.noDisposable());

boolean isValid = strictJudge.isValid("user@example.com");

Custom rules

import dev.nightowl.mailjudge.rules.Ruleset;
import dev.nightowl.mailjudge.rules.impl.*;

// Build a custom ruleset
Ruleset customRuleset = Ruleset.builder()
    .rule(new SyntaxRule())
    .rule(new LengthRule())
    .rule(new DomainRule())
    .rule(new MxRecordRule())
    .build();

MailJudge judge = MailJudge.withRuleset(customRuleset);

Predefined rulesets

Standard (default)

• Syntax validation
• Length validation (RFC 5321)
• Local-part validation
• Domain validation
• TLD validation

Strict

• All standard rules
• Optional MX record lookup (requires DNS access)

No Disposable

• All standard rules
• Blocks known disposable email providers (local caching of the list)

Complete

• All rules including MX and disposable checks
• Most comprehensive validation

Available rules

Rule	Description
SyntaxRule	Basic @ symbol and structure checks
LengthRule	RFC 5321 length limits
LocalPartRule	Local-part format validation
DomainRule	Domain structure validation
TldRule	Top-level domain validation
DisposableRule	Disposable email detection
MxRecordRule	DNS MX record lookup (network-dependent)

Building and running

Requirements

• Java 17 or higher
• Gradle 8.x

Common tasks

# Build the library
./gradlew build

# Run tests
./gradlew test

# Generate Javadoc
./gradlew javadoc

Creating custom rules

Implement the Rule interface:

import dev.nightowl.mailjudge.rules.Rule;

public class CustomRule implements Rule {
    @Override
    public boolean validate(String email) {
        // Your validation logic
        return true;
    }

    @Override
    public String getErrorMessage() {
        return "Custom validation failed";
    }
}

Examples

Batch validation

List<String> emails = Arrays.asList(
    "user1@example.com",
    "user2@example.com",
    "invalid@"
);

MailJudge judge = MailJudge.withRuleset(Rulesets.standard());

Map<String, ValidationResult> results = emails.stream()
    .collect(Collectors.toMap(
        email -> email,
        judge::validate
    ));

Detailed error messages

ValidationResult result = MailJudge.verify("invalid..email@example.com");

if (!result.isValid()) {
    System.out.println("Email: " + result.getEmail());
    result.getErrors().forEach(error -> 
        System.out.println("  - " + error)
    );
}

Why not use regular expressions?

• Better performance in many cases by avoiding regex compilation and backtracking
• Clearer, more maintainable parsing logic
• Easier to extend and reason about for custom rules

License

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

Contributing

Contributions are welcome. Please open an issue or submit a pull request with a clear description of the change and tests where appropriate.