checking emails

You have got a site hosted on a shared server - you may be blacklisted.

If you want to run serious email camapigns, it is always a good idea to go for third party services. Specially if your site is hosted on a shared server, you may quickly find out that your IP is registered as SPAM.

Check this website out:
http://www.mxtoolbox.com

Enter you domain name, and the site will look up for you - results may be a bad surprise.