You can create custom search folders based on categories to organize emails. Not sure how efficient this is with a large amount of mail.
Use one of the following to create custom search folder:
Under the Folder tab in Outlook, click New Search Folder
Use the keyboard shortcut CTRL+SHIFT+P
In the sidebar of the folder hierarchy, you should have a folder called Search Folders, right click on it to get the New Search Folder option
Here is the Microsoft documentation on creating them for Outlook 2010.