check_dns.sh

#!/bin/bash
set -e
# dnsだけ調べる
# usage
# ./check_dns.sh hoge@example.com

domain=`echo $1 | cut -d@ -f2`
mxrecords=`dig +short $domain. mx | wc -l`
if [ "$mxrecords" -ge "1" ];then
    echo ok
else
    echo not found
fi

email-ping.rb

#!/usr/bin/env ruby
#
# = Email Ping
#
# Check to see if an email address exists by looking up MX records and connecting
# to the address's home SMTP server. It then starts to send a message to the address
# but quits before the message is actually sent.

require 'resolv'
require 'net/smtp'

address = ARGV[0].chomp
domain = address.split('@').last
dns = Resolv::DNS.new

mx_records = dns.getresources domain, Resolv::DNS::Resource::IN::MX
mx_server  = mx_records.first.exchange.to_s

Net::SMTP.start mx_server, 25 do |smtp|
  smtp.helo "loldomain.com"
  smtp.mailfrom "test@loldomain.com"

  begin
    smtp.rcptto address
    puts "#{address} => OK"
  rescue Net::SMTPFatalError => err
    puts "#{address} => NG"
  end
end

# vim: set ft=ruby ts=2 sw=2 :