el capitan mail

I am running an iMini from 2010. I have upgraded to all the latest versions for the mac until El Capitan and my email messages have disappeared from the past several years. I am very upset about this situation since there are valuable conversations that have been lost!!!!! ***!!! Did you hide some settings that are not known to users?

On another note, the previous version wiped all of my 'digital movies' that I had redeemed online and are no longer available on my mac. They are still available on my iPad and on the AppleTV Get your **** together. I was a big Apple Fan.