Missing The Most Important Folder In My Inbox

Now how does a folder with thousands of emails disappear to? I am missing one of the most important emails ever in my inbox. I had this once happen before but found it in another folder. This time I can't find it. Luckily I have a program that backed up my information 3 days ago. I will be able to recover most of that folder but will be missing any emails I put in that folder for the last 3 days. I just want to cry. I don't even know where to begin to restore just that folder of emails.

Stefani