Because we were sending loads of messages we had problems with AOL and Yahoo who both thought it might be spam and started blocking us. I eventually got it sorted out and got us 'white listed' but then 1 aol member accidently clicked his spam button and bang we were blacklisted again. He sent me an apology which I forwarded to aol and they sorted it out but it took a couple of weeks. I then decided to go for a professional service that is white listed. It also gives me a detailed breakdown of who opened my messages, how often, and if they forwarded it to anyone else or if the clicked any of the links in the message. all for under $6 per month for up to 500 messages.