Outlook provides 20 default
categories for you, but you may want to create your own. Here's how:
Select one or more messages to
assign to a category.
Choose File, Categories (or
right-click the items and choose Categories from the shortcut menu).
Click in the Item(s) Belong To
These Categories box and type the new category name (if you want to type
more than one, separate the names with a comma).