I did some checking and found that Bell South does in fact, filter Port 25 as normal procedure.
This is to stop spam. The only way around it, is for you to contact Road Runner and also
Yahoo Small Biz to see if they have an Alternate Port to use in place of Port 25 ... if they do
just set that port number into your email client, such as Outlook
Try Port #26 or Port #587 or Port #2500