According to my brief Google search it sounds like there was an issue with their email storage platform. Cox.net says they're replacing their email storage platform equipment. It sounds like they had an issue with their email storage platform and are working on replacing it. Personally I would recommend moving away from your ISP's email account in favor of one of the many free email services out there to avoid situations like this (Concise article with other reasons to switch email providers).
For more on the outage:
Thanks for the advice and links.