I do not receive all my e-mailson all my devices. I seem to get them all on my iPhone 5s, but not all show up on my iPad and iMac. they are all set up the same. Any Ideas on what is going on and what I can do to remedy this? thanks

I have an iMac with OS X Lion 10.7.5,an iPhone 5s with iOS 7.1.2 and an iPad with iOS 7.1.2. all software is up to date. My problem is I do not receive all my e-mail on all 3 devices all the time. I seem to get them on my phone , but not all show up on my iMac or iPad. Any ideas as to what is going on and what can I do to resolve this issue? thanks