note 24146 rejected from ref.mail by maxim

I need to send several emails (about 10,000). I used the mail() function to test on 500 and it worked. But ever since no call to the mail () works. It gives no error but I don't receive any of the emails been sent. I assume the server where I host the site has put some sort of restriction on my account. I called them but they don't seem to know what I am talking about. Does anybody knows how can I avoid this? Thanks for your help!