Emails won't come through even though I know there are some.

I use Mac Mail and I never seemed to have a problem before. Recently, I've been refreshing my emails and none of them are being downloaded. I know there are some emails waiting for me because I've checked on my phone but my iphone is also starting to not work as it wont download the content of my email anymore, just the title, who its from, when etc. I'm not worried about that at the minute but I am concerned about my mac. Anyone know whats going on?