You said you checked your blocked senders site, is that the same as the spam file? If not, check it. Put those sites from which you want to receive mail in your contacts list.
I use Outlook for my AT&T mail. So, that means that all my AT&T mail goes through Yahoo. Yahoo/AT&T seems to randomly choose mail to mark as spam. One day it's spam and the next day, it's not. So, you have to go to the AT&T site to see what they've chosen as spam, as it won't show up on your Outlook.