iPhone iOS 7 and Macbook Air Mavericks, deleting hotmail emails to POP folder! Help!

I have an iPhone using the iOS 7 and a Macbook Air using Mavericks (although I'm not sure how relevant this is) and both are set up to receive and send emails to my hotmail account.. Every so often (I think a month or so) I check my emails on either device to find that my hotmail emails have been deleted from my device. When I then log on to hotmail's website, they have been moved to a POP folder, so I then have to move my emails to my inbox and the phone and macbook start receiving them again, very strange! I assume somewhere the settings are wrong, on either my macbook or phone (or possibly hotmail itself). If you have any ideas, please help me, it's getting very annoying!

Thanks!