When I start my outlook 2013 client the email count in my Inbox starts going down like emails are getting deleted?

I setup an account for my Hotmail email in the outlook 2013 client and downloaded about ten years worth of emails (about 190000) in February of 2015. Then when I started up my outlook client today 4/5/2015 it should be downloading about two months of emails since February but instead the Inbox email count is starting to go down and now is at about 175000 emails

Anyone know why this is happening? It seems like its deleting emails rather than downloading new ones according to the Inbox email count? February 2015 was about 190000 and now its about 175000.

Any explaination of what might be going on?

Thanks!

only option i can think of is auto archive. please check for any auto archive settings enabled on your outlook 2013.