iphone message--cannot get mail.connection to server failed
I have been receiving my yahoo.email to my iphone 4 for months now, but this week its stopped working, It appears to be set up on the iphone, but when I try to get mail , I get the message cannot get mail, connection to server failed. I am getting my gmail to the iphone and some yahoo emails! I just don't understand this ! can anyone enlighten me?
iPhone 4