It depends on why they're not getting there. It could be anything from aggressive spam filtering (once a few people mark your messages as spam, you can get put on a blocked senders list), to failed address etc. Look at your error logs, and make sure that you're failing gracefully (but verbosely to the logs). Then if it's in the budget, setup a hotmail account or 20 to send test messages to. On top of that, godaddy limits outbound mail blasts, you'll have to get the number from them, I've heard everything from 500 to 1200 per day given as a limit on their side. The fix to that would be to use multiple addresses for your email blasts so that each is sending fewer than the maximum; or use a host that doesn't set arbitrary limits on communication. On the bright side, there are a lot of hosts that are cheaper, but provide better service. Research for horror stories before picking a host, they're very easy to find because angry ex customers of hosting companies go to other companies and use some portion of their new space complaining about the ordeal with the last company.