I would of proposed using GoDaddy's e-mail marketing services however I'm assuming you use purchased or harvested e-mail lists?
If the quality of your e-mail list itself is poor you will get blacklisted either way due to high bounce rates.
In regards to ways of sending bulk e-mails there are many services around the web, there's a lot of e-mail marketing software around too.
Have a search on google.com
Hope this helps.