Open Outlook
Go to File
Select Options
Click Mail
Under Compose messages, click Stationery and Fonts
Choose the font size you want for new emails, replies, and plain text messages
Click OK
To make the reading pane text bigger, open an email
Use the zoom slider in the lower-right corner
Or press Ctrl and scroll up with your mouse
To change the message list font, go to View
Select View Settings
Click Other Settings
Adjust the font size for columns and rows
Click OK
To make the Outlook interface bigger, change your Windows display scaling
Open Windows Settings
Go to System
Select Display
Increase Scale and layout
Restart Outlook if needed