It's easy enough to change fonts in Outlook's Inbox or other folders using View-View Settings-Other Settings-Column Font and Row Font, but a customer wanted to change the font in the Navigation Pane. This turned out to be tricky. Everything I found pointed to changing to fonts inside the folder or was otherwise useless. I finally found the answer on page 4 of a thread at this link:
The procedure is to change the font in Windows, not in Outlook.
- Click the Windows logo in the bottom right corner of the screen.
- Click thee “Gear” icon to bring up Settings.
- Click Ease of Access.
- Slide the slide bar to adjust the size of the text.
- Click Apply.
- Go back to Outlook
- Click the “<” icon at the top of the Navigation Pane to close it.
- Click the “>” icon at the top of the Navigation Pane to reopen it.
- Repeat the procedure until you see a text size that you like.
Note that this changes the text size for all of the menus in Windows and your applications, including the “Ribbon” in MS Office. It also changes the text size in your browser tabs and the size of text and images displayed in your browser. All browsers (Edge, IE, Firefox, Chrome) are affected.