Emails are deleting daily without me doing so. I lost years worth of emails how do I retrieve them???

My emails are gone from my hotmail account. I first noticed on my iPhone when it would only load daily received emails, all old emails no longer showed up on my phone. So when I logged in on my computer all emails are being deleted daily I realized because my deleted folder included the previous days emails which I never deleted. What's going on and how can I retrieve these very important emails???