Rails · Ruby

Block disposable email in Rails

Custom ActiveModel validator on User#email. Works with Devise, Sorcery, or hand-rolled signup controllers.

The code

# app/validators/not_disposable_email_validator.rb
class NotDisposableEmailValidator < ActiveModel::EachValidator
  PIISEND_URL = "https://api.piisend.com/api/v1/intelligence/email"

  def validate_each(record, attribute, value)
    return if value.blank?

    begin
      response = HTTParty.post(
        PIISEND_URL,
        headers: {
          "Authorization" => "Bearer #{ENV['PIISEND_API_KEY']}",
          "Content-Type" => "application/json",
        },
        body: { email: value }.to_json,
        timeout: 5,
      )
      if response.success? && response.parsed_response.dig("signals", "disposable")
        record.errors.add(attribute, "Please use a permanent email address.")
      end
    rescue StandardError
      # fail open
    end
  end
end

# app/models/user.rb
class User < ApplicationRecord
  validates :email, not_disposable_email: true
end

API key

Set `PIISEND_API_KEY` in credentials or ENV — use `dotenv-rails` locally.

Fail-open vs fail-closed

Rescue block skips validation on errors.

Pair with verification

Add the validator before Devise's `:validatable` or inside a custom RegistrationsController.

Send verification email with Piisend

After blocking disposable addresses, send OTP and verification mail through the same Piisend account. One API key for intelligence checks and transactional sends.

Get API keyQuickstartAll guides