Windows Mail is a year behind

I use the Mail app in Windows to receive and send emails, and the same account is also synced with my iPhone. The phone is receiving all of my new emails as normal, but suddenly the inbox in Mail is only showing emails that I received up to June 18th last year, approximately a year ago. The strange thing is, the emails at the top in my inbox are only marked '18 Jun', '17 Jun', '15 Jun' etc., but then after the first four they are marked 11/06/2014, 10/06/2014 etc., even though those messages are from the same year. It looks like it's somehow decided that those four top emails are from this year, not last year, and moved them to the top, but there's no sign of the emails that are actually from this year, and I'm not receiving any new ones. I'm a bit concerned about all of my emails from the last year being missing, because obviously they include some important stuff. Does anyone know what's going on?