Email Validator Service

A high-performance, cost-effective email validation service designed for indie hackers and small startups. The service validates email addresses in real-time, checking syntax, domain existence, MX records, and detecting disposable email providers. The main focus is on precision instead of recall, meaning instead of edge cases the focus is on having the biggest coverage.

🌐 Website: https://rapid-email-verifier.fly.dev/

🚀 API https://rapid-email-verifier.fly.dev/api/validate

This is a completely free and open source email validation API that never stores your data. Built to support solopreneurs and the developer community. Features include:

Zero data storage - your emails are never saved!
GDPR, CCPA, and PIPEDA compliant
No authentication required
No usage limits
Quick response times
Batch validation up to 100 emails

Features

✅ Syntax validation
🌐 Domain existence check
📨 MX record validation
🚫 Disposable email detection
👥 Role-based email detection
✍️ Typo suggestions
📊 Real-time monitoring
🔄 Batch processing support

Validation Examples

Note on Validation Approach: While email RFCs (5321, 5322) define extensive rules for valid email formats, many of these rules are not practically enforced by modern email servers. Our validation takes a practical approach, focusing on rules that are actually enforced by major email providers. For example, we don't support quoted strings in local parts ("john doe"@example.com) even though they're technically valid according to RFC, as they're rarely supported in practice and often cause issues.

Valid Email Formats

// Standard email
{
  "email": "[email protected]",
  "validations": {
    "syntax": true,
    "domain_exists": true,
    "mx_records": true
  },
  "status": "VALID"
}

// Email with plus addressing
{
  "email": "[email protected]",
  "validations": {
    "syntax": true,
    "domain_exists": true,
    "mx_records": true
  },
  "status": "VALID"
}

// International email (Unicode)
{
  "email": "用户@例子.广告",
  "validations": {
    "syntax": true,
    "domain_exists": true,
    "mx_records": true
  },
  "status": "VALID"
}

// Hindi characters
{
  "email": "अजय@डाटा.भारत",
  "validations": {
    "syntax": true,
    "domain_exists": true,
    "mx_records": true
  },
  "status": "VALID"
}

Invalid Email Formats

// Missing @ symbol
{
  "email": "invalid-email",
  "validations": {
    "syntax": false
  },
  "status": "INVALID_FORMAT"
}

// Double dots in local part
{
  "email": "[email protected]",
  "validations": {
    "syntax": false
  },
  "status": "INVALID_FORMAT"
}

// Spaces in quotes (not supported)
{
  "email": "\"john doe\"@example.com",
  "validations": {
    "syntax": false
  },
  "status": "INVALID_FORMAT"
}

// Multiple @ symbols
{
  "email": "user@[email protected]",
  "validations": {
    "syntax": false
  },
  "status": "INVALID_FORMAT"
}

Special Cases

// Disposable email detection
{
  "email": "[email protected]",
  "validations": {
    "syntax": true,
    "domain_exists": true,
    "mx_records": true,
    "is_disposable": true
  },
  "status": "DISPOSABLE"
}

// Role-based email detection
{
  "email": "[email protected]",
  "validations": {
    "syntax": true,
    "domain_exists": true,
    "mx_records": true,
    "is_role_based": true
  },
  "status": "PROBABLY_VALID"
}

Batch Validation

// Request
POST /api/validate/batch
{
  "emails": [
    "[email protected]",
    "invalid-email",
    "[email protected]",
    "[email protected]"
  ]
}

// Response
{
  "results": [
    {
      "email": "[email protected]",
      "validations": {
        "syntax": true,
        "domain_exists": true,
        "mx_records": true
      },
      "status": "VALID"
    },
    {
      "email": "invalid-email",
      "validations": {
        "syntax": false
      },
      "status": "INVALID_FORMAT"
    },
    {
      "email": "[email protected]",
      "validations": {
        "syntax": true,
        "domain_exists": false
      },
      "status": "INVALID_DOMAIN"
    },
    {
      "email": "[email protected]",
      "validations": {
        "syntax": true,
        "domain_exists": true,
        "mx_records": true,
        "is_role_based": true
      },
      "status": "PROBABLY_VALID"
    }
  ]
}

Tech Stack

Go 1.21+
Redis (caching, only for domains, not email addresses)
Prometheus (metrics)
Grafana (monitoring)
Docker & Docker Compose

Prerequisites

Go 1.21 or higher
Docker and Docker Compose
Git
VSCode (recommended)

Development Environment Setup

1. Install Go

macOS

# Using Homebrew
brew install go

# Verify installation
go version  # Should show go version 1.21 or higher

Linux (Ubuntu/Debian)

# Add Go repository
sudo add-apt-repository ppa:longsleep/golang-backports
sudo apt update

# Install Go
sudo apt install golang-go

# Verify installation
go version

Windows

Download the installer from Go Downloads
Run the installer
Open Command Prompt and verify:

go version

2. Configure Go Environment

Add these to your shell profile (~/.bashrc, ~/.zshrc, etc.):

# Go environment variables
export GOPATH=$HOME/go
export PATH=$PATH:$GOPATH/bin

Reload your shell or run:

source ~/.bashrc  # or ~/.zshrc

3. Install Docker

macOS

Download Docker Desktop for Mac
Install and start Docker Desktop
Verify installation:

docker --version
docker-compose --version

Linux

# Install Docker
curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh

# Install Docker Compose
sudo apt install docker-compose

# Start Docker
sudo systemctl start docker

# Add your user to docker group (optional)
sudo usermod -aG docker $USER

# Verify installation
docker --version
docker-compose --version

Windows

Download and install Docker Desktop for Windows
Enable WSL 2 if prompted
Start Docker Desktop
Verify in Command Prompt:

docker --version
docker-compose --version

4. VSCode Setup

Install VSCode
- Download from Visual Studio Code
- Install for your platform

Install Required Extensions

# Essential Extensions
- Go (by Go Team at Google)
- Docker (by Microsoft)
- GitLens (by GitKraken)
- Remote Development (by Microsoft)

# Recommended Extensions
- Error Lens
- Go Test Explorer
- YAML
- Markdown All in One

Configure Go Extension After installing the Go extension:
1. Open Command Palette (Cmd/Ctrl + Shift + P)
2. Type "Go: Install/Update Tools"
3. Select all tools and click OK
This will install:
- gopls (Go language server)
- dlv (debugger)
- golangci-lint (linter)
- goimports (code formatter)
- and other essential Go tools

VSCode Settings Create or update .vscode/settings.json:

{
  "go.useLanguageServer": true,
  "go.lintTool": "golangci-lint",
  "go.lintFlags": ["--fast"],
  "editor.formatOnSave": true,
  "[go]": {
    "editor.defaultFormatter": "golang.go",
    "editor.codeActionsOnSave": {
      "source.organizeImports": true
    }
  }
}

Debugging Setup Create .vscode/launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Launch Email Validator",
      "type": "go",
      "request": "launch",
      "mode": "auto",
      "program": "${workspaceFolder}",
      "env": {},
      "args": []
    }
  ]
}

5. Install Additional Tools

# Install golangci-lint
go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest

# Install air for hot reload (optional)
go install github.com/cosmtrek/air@latest

# Install mockgen for testing
go install github.com/golang/mock/mockgen@latest

Setup

Clone the Repository

git clone https://github.com/umuterturk/email-verifier.git
cd email-verifier

Install Dependencies

go mod tidy

Start Monitoring Stack

docker-compose up -d

Build and Run the Service

go build
./emailvalidator

The service will be available at:

API: http://localhost:8080
Metrics: http://localhost:8080/metrics
Grafana: http://localhost:3000 (admin/admin)
Prometheus: http://localhost:9090

Development

Project Structure

.
├── cmd/                    # Command line tools
├── internal/              
│   ├── api/               # HTTP handlers
│   ├── middleware/        # HTTP middleware components
│   ├── model/            # Data models
│   ├── repository/       # Data access layer
│   └── service/          # Business logic
├── pkg/
│   ├── validator/        # Email validation logic
│   ├── monitoring/       # Metrics and monitoring
│   └── cache/           # Caching implementation
├── test/                 # Unit, integration and acceptnce tests
└── config/               # Configuration files

Running Tests

Run All Tests (excluding load tests)

go test ./... -v -skip "Load"

Run Tests with Race Detection

go test -race ./... -skip "Load"

Race detection is crucial for identifying potential data races in concurrent code. It's automatically run in CI/CD pipelines and should be run locally before submitting changes.

Common race conditions to watch for:

Concurrent map access
Shared variable access without proper synchronization
Channel operations
Goroutine lifecycle management

Run Load Tests

go test ./test/load_test.go -v

Code Quality

Run Linter

golangci-lint run

Format Code

go fmt ./...

Check for Common Mistakes

go vet ./...

Continuous Integration

The project uses GitHub Actions for CI/CD with the following checks:

Unit tests with race detection
Integration tests
Acceptance tests
Code linting
Code formatting
Security scanning
Dependency updates

All these checks must pass before code can be merged into the main branch.

Testing

The project includes several types of tests:

API Testing Script

# Run the comprehensive API test suite
./test_api.sh

Disclaimers

Accuracy Disclaimer

The results provided by this service are based on best-effort validation and should be treated as recommendations rather than absolute truth. Several factors can affect the accuracy of results:

Domain DNS records may change
Temporary DNS resolution issues
Network connectivity problems
Email server configuration changes
Rate limiting by email servers
Syntax validation differences between email providers

Legal Disclaimer

This service is provided "as is" without any warranties or guarantees of any kind, either express or implied. The validation results are for informational purposes only and should not be considered legally binding or definitive. We expressly disclaim any liability for damages of any kind arising from the use of this service or its results. Users are solely responsible for verifying the accuracy of email addresses through additional means before using them for any purpose.

Name		Name	Last commit message	Last commit date
Latest commit History 48 Commits
.github		.github
.vscode		.vscode
config		config
internal		internal
pkg		pkg
static		static
tests		tests
.gitignore		.gitignore
.golangci.yml		.golangci.yml
Dockerfile		Dockerfile
LICENSE		LICENSE
README.md		README.md
docker-compose.yml		docker-compose.yml
email_providers.csv		email_providers.csv
fly.toml		fly.toml
go.mod		go.mod
go.sum		go.sum
grafana-dashboard.json		grafana-dashboard.json
main.go		main.go
openapi.yaml		openapi.yaml
prometheus.yml		prometheus.yml
rapidapi-doc.md		rapidapi-doc.md
settings.json		settings.json
test_api.sh		test_api.sh

License

umuterturk/email-verifier

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Email Validator Service

Features

Validation Examples

Valid Email Formats

Invalid Email Formats

Special Cases

Batch Validation

Tech Stack

Prerequisites

Development Environment Setup

1. Install Go

macOS

Linux (Ubuntu/Debian)

Windows

2. Configure Go Environment

3. Install Docker

macOS

Linux

Windows

4. VSCode Setup

5. Install Additional Tools

Setup

Development

Project Structure

Running Tests

Code Quality

Continuous Integration

Testing

API Testing Script

Disclaimers

Accuracy Disclaimer

Legal Disclaimer

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Resources

License

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