The first search field shown in the Overview page never brings up any result when searching our email database.
It matches emails exactly as they are typed (case-insensitive) then the search box will search that product version in LimeLM and find all matching product keys. You need to be more specific if it's actually not working as you expect -- you need to tell us which emails aren't working.
And of course the advanced search lets you search for product keys while specifying wildcard characters (*). Meaning you don't need to know the exact email. For example "*@microsoft.com" would find all product keys that have a Microsoft email address.
And of course you can search by other fields as well in the advanced search page. Can you tell me the workflow that you have that this is causing problems?