I have a strange issue in Yahoo mail around a year. Mails sent to yahoo through my mail servers are temporary deferred. But they will be send after several sending attempts. So my mail server queue is increasing due to yahoo mail problem. Error message says that's mail are temporary deferred. But mails are properly sending to Gmail and other mail servers . I checked my mail server for open relay and other errors. Everything is all right. Do any of system administrators has faced similar situation ? I am using Postfix mail server.