validate.rb

def get_domain email
  return unless email_format_valid?(email)

  email.split("@").last
end

def get_mxs email
  return unless email_format_valid?(email)
  
  domain = get_domain(email)
  cache("mxs_#{domain}") do
    Resolv::DNS.open do |dns|
      ress = dns.getresources(domain, Resolv::DNS::Resource::IN::MX)
      ress.map do |r|
        [
          r.exchange.to_s,
          IPSocket.getaddress(r.exchange.to_s),
          r.preference
        ]
      end
      rescue Exception => e
        puts "Failed lookup: #{e}"
        nil
      end
	end
	
end

def get_mx email
  get_mxs(email)&.first&.first
end

def base_email(email)
  return unless email_format_valid?(email)

  a = email.split("@", 2)
  "#{a[0].split("+").first.strip}@#{get_domain(email)}"
end

def email_format_valid?(email)
  return nil unless email =~ /\A[a-zA-Z0-9.!\#$%&'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)+\z/
  true
end

def free_esp?(domain)
  return nil unless domain

  domains = remote.get("https://gist.githubusercontent.com/ammarshah/f5c2624d767f91a7cbdc4e54db8dd0bf/raw/660fd949eba09c0b86574d9d3aa0f2137161fc7c/all_email_provider_domains.txt").cache.body.split("\n")
  domains.include?(domain.downcase)
end

def smtp_validation(email)
  return unless get_mx(email).present?

  remote.get("https://crcr.me/?email=#{email}&mx=#{get_mx(email)}").cache(1.hour.from_now).json
end

def business_information(email)
  return unless email_format_valid?(email)

  remote.get("https://sso.serial.im/r/bin:logo-api/search?q=#{email}").cache.json
end

ret = {}
ret[:query] = params[:email]
if ret[:query].present?
  ret[:email] = base_email(ret[:query])
  ret[:domain] = get_domain(ret[:email])
  ret[:is_email_format] = email_format_valid?(ret[:email])
  ret[:free_esp] = free_esp?(ret[:domain])
  ret[:smtp_validation] = smtp_validation(ret[:email])
  ret[:is_valid] = ret[:smtp_validation] && ret[:smtp_validation].dig("valid") == "valid" || false
  ret[:business_info] = ret[:free_esp] ? nil : business_information(ret[:email])
  ret[:mxs] = get_mxs(ret[:email])
  ret[:mx] = get_mx(ret[:email])
  
else
  ret[:error] = "?email= is required"
end

send_json(ret)