Hopefully they checked it before issuing it... and you need to make sure all your appropriate DNS entries are made, you have your bounced and unsubscribe addresses configured for use before you get to far, or you may find that HotMail will block you again. You may also simply find that your hosting providers entire IP range is in their block list filter. Over the last 8 years, HotMail has been the biggest headache trying to get mail to go through. They'd prefer you pay to be on their list, or use a major mail service that already has.