Checks whether a mail is probably a google apps email

check.rb

#!/usr/bin/env ruby

require 'resolv'
require 'public_suffix'


email  = ARGV[0]
domain = email.split("@").last

servers = %w(googlemail.com, google.com)

# get the server with lowest preference number -> highest priority!
mail_server = Resolv::DNS.open.getresources(domain, Resolv::DNS::Resource::IN::MX).min_by{|s| s.preference}

# grab TLD and compare with our list of servers
is_valid =  mail_server.nil? ? false: servers.include?( PublicSuffix.parse(mail_server.exchange.to_s).domain)

puts "Is google apps:", is_valid