How to Validate Emails in Ruby on Rails with Mailchk

Rails makes custom validation easy with Active Model validators. This guide shows how to integrate Mailchk email validation using a service object, a custom validator, and controller-level checks.

Step 1: Service Object

# app/services/email_validator.rb
class EmailValidator
  API_URL = "https://api.mailchk.io/v1/check"

  def self.validate(email)
    new(email).validate
  end

  def initialize(email)
    @email = email
  end

  def validate
    cached = Rails.cache.read(cache_key)
    return cached if cached

    result = call_api
    Rails.cache.write(cache_key, result, expires_in: 24.hours)
    result
  end

  private

  def call_api
    uri = URI(API_URL)
    http = Net::HTTP.new(uri.host, uri.port)
    http.use_ssl = true

    request = Net::HTTP::Post.new(uri)
    request["Content-Type"] = "application/json"
    request["X-API-Key"] = Rails.application.credentials.mailchk_api_key
    request.body = { email: @email }.to_json

    response = http.request(request)
    JSON.parse(response.body)
  rescue StandardError
    { "valid" => true, "disposable" => false }
  end

  def cache_key
    "email_validation:#{Digest::MD5.hexdigest(@email)}"
  end
end

Step 2: Custom Active Model Validator

# app/validators/real_email_validator.rb
class RealEmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    return if value.blank?
    result = EmailValidator.validate(value)

    unless result["valid"]
      record.errors.add(attribute, "does not appear to be valid")
      return
    end

    if result["disposable"]
      record.errors.add(attribute, "cannot be a disposable address")
    end

    if options[:block_free] && result["free_email"]
      record.errors.add(attribute, "must be a work email address")
    end
  end
end

Step 3: Use in Your Model

# app/models/user.rb
class User < ApplicationRecord
  validates :email,
    presence: true,
    uniqueness: true,
    real_email: true

  # B2B: also block free providers
  # validates :email, real_email: { block_free: true }
end

Controller-Level Validation

class RegistrationsController < ApplicationController
  def create
    result = EmailValidator.validate(params[:email])

    if result["did_you_mean"]
      render json: { suggestion: result["did_you_mean"] }, status: 422
      return
    end

    if result["disposable"]
      render json: { error: "Disposable emails not allowed" }, status: 422
      return
    end

    @user = User.new(user_params)
    if @user.save
      render json: @user, status: :created
    else
      render json: { errors: @user.errors }, status: 422
    end
  end
end

Background Validation with Active Job

# app/jobs/validate_email_job.rb
class ValidateEmailJob < ApplicationJob
  queue_as :default

  def perform(user_id)
    user = User.find(user_id)
    result = EmailValidator.validate(user.email)

    if result["disposable"]
      user.update(email_status: "disposable")
    elsif result["valid"]
      user.update(email_status: "verified")
    else
      user.update(email_status: "invalid")
    end
  end
end

Best Practices

• Cache with Rails.cache — use Redis in production.
• Fail open — never block a signup because the API is temporarily unreachable.
• Use Rails credentials — more secure than plain ENV vars for API keys.
• Show typo suggestions — did_you_mean converts better than a hard rejection.

Getting Started

Sign up for a free Mailchk account. 200 validations/month free, sub-50ms response time.