Use the Search box at the top of Outlook
Type the folder name you are looking for
Check the folder list in the left pane
Expand collapsed mailbox folders or subfolders
Use the folder search feature if available in your Outlook version
Right-click the mailbox name and choose to expand all folders
Look under Favorites if the folder was pinned there
Use Ctrl+Y in Outlook desktop to open the Go To Folder dialog
Scroll through the folder pane if the folder is nested deeply
Check archived, shared, or secondary mailboxes if the folder is not in your main mailbox