Yahoo loves playing defer game. Before the advent of new CEO, it was just temporarily defer (3 response messages randomly rotating) but now it's permanently defer and this would happen even for servers sending 10 mails/day globally. No amount of being the good guy helps as most of the time contacting postmaster would just waste too much time with same end result. So what does one do? Answer is simple. Do unto Yahoo what Yahoo does unto you. This is provided you are dead sure you do not host spammer. Fill up their form from whatever crap url that they send in response. Once you get a reply (not auto response but a semi bot reply with cse ID) then be brave and put following in Exim from WHM deny message = Contact Yahoo With Case # XXXXXXX For Delivery Failure Or Stop Using Yahoo hosts = *yahoo.com log_message = Yahoo Blocked Grep your exim log to see if it is being blocked. If yes then reply to postmaster that till they unblock and stop their stupidity entire yahoo network is blocked. Yahoo is biggest abuser of 4xx codes on WEB. So give them a stronger medicine with 5XX rsponse with a specific bounce message. Just sit back and wait. Your problems will be fixed in few days/weeks. Imagine a syndicate of 1000 servers doing this and sending 1 million such response a day. Many Paidbizmail users/Yahoo Hosted Zimbra users would also be hit and they would definitely start f****** Yahoo support. Then their BOFH ( http://en.wikipedia.org/wiki/BOFH ) Admins would wake up and either set things right or Yahoo starts llosing on PAID clients. That's what the idea of entire excercise is. Hit Yahoo where it would hurt them most --- Finances. This is the best way to deal with Yahoo. Why should we care about mails coming in from Yahoo when they dont care about accepting mails. We talked to Datacenter also and they said Yahoo is know to permanently defer mails from even new servers with clean IP's and sending just few mails/day globally. Yahoo Sucks in short.