How do I fix this read/unread problem with my Samsung Blackjack?

I just inherited an old Samsung Blackjack at work. I can get all of my Outlook emails, read them, respond to them, sort them into folders etc. But when I get back into the office, they are all unread in my email box. They will even be in the folders I sorted them into, but unread. Does anyone know how to solve this? Thanks!