Me and my father switched to cox about a month ago and haven't been able to check our yahoo mail since. We can get to yahoo, we can log into our accounts, but the second we press that mail button nothing works.
My father contacted them a little while back and actually got a real person who told him to do something really stupid (hit reload, turn off your firewall, something like that) and disconnected as soon as dad tried.
Apparently this isn't the first time cox has blocked a site. I was told they blocked craigslist a while back because it was in compitition to some website cox tried to launch, but I don't have any details.
I see it as bad service to block a popular email host. I'm more attached to my yahoo account than I am cox (and having to reset the cable modem every 2 hours).
Edit: Appears I was wrong, apparently it isn't cox intentionally blocking yahoo. Thanks for your help.