said by SmokChsr:
Good luck trying to get it removed, the last time I tried (back when AT&T did their own email)...
That's a good point. If the email sending is blocked not the IP, shouldn't the OP be contacting Yahoo?
Also NormanS, made a good point too, you want to find out why you are blocked. If you are not the admin or the sender, you need to get to them and see if you NDR mesages or if the connection logs hold any clue to what is going on. I don't have my resources but there are many places online to check to see if your server is on block lists and some say why.