Windows Live Mail quit sending bulk mailing

I am on white list with Earthlink to send bulk mail, which I have been doing for years, most recently the end of May. This week, it will not go. I get no error message from Earthlink, so I think the problem is not with them. I am sending and receiving other emails with no problems The bulk mail, with 700 recipients just sits in the out box, saying "sending mail." It can sit there as long as 20 minutes saying "sending mail," and nothing happens. No error message. What could be the problem? It's on a PC with Windows 7. I have made no changes in the last month. Only Windows updates. Thank you for any ideas.