I accidentally marked a valid email address as spam.?

I accidentally marked a valid email address as spam. Now I'm no longer receiving the email from the company. I've checked the spam folder, and the daily email I used to receive from the company is not even being routed to that folder. I've gone to the Options setting, and tried to search for the email address, to mark it as not spam, but it's not in the list. I just noticed that it's indicating 500 of 500 at the top of the spam email list. Apparently, I've exceeded the 500 address limit, but it's still allowing me to block email and mark it as spam. The problem is, it seems to be going into some type of black hole listing that I can't get to, nor does it route it to the spam folder. Any help would be greatly appreciated.