Users aren't usually very good about cleaning out their mailboxes. It's not uncommon for them to have a couple of hundred messages in the Inbox, if not more. As the number of messages in the Inbox grows, finding a particular message can become a real challenge.
Outlook offers several methods for sorting folder contents. Click the From or Subject column headers to sort messages by sender or subject. Or use the Group By function to group messages by a selected column—just right-click a column header and choose Group By This Field. To restore the previous view, right-click the field in the Group By Box, and choose Don't Group By This Field. Right-click the column header again, and choose Group By Box to hide that box.
Another solution is to create a rule that colors the message header. Follow these steps:
Outlook colors the header for all messages that meet the specified condition.