IPhone 5 Can't connect to my Yahoo mail

Get error message saying "connect cannot connect to Yahoo server...Try later I have been trying for 24 hrs. Went to Apple store and someone else there having same problem....They took our phones and gave us new ones.....Same problem......They took a demo phone and used one of the store persons e-mail and there was no problem. It appears to be happening on just some e-mail addresses...Anyone else with this problem? Any solution

Getting Yahoo customer service is "yahoo no service"