Open Outlook
Go to the email you want to read
Use the zoom slider at the bottom right of the message window
Move the slider to the right to increase text size
Press Ctrl and scroll up with your mouse wheel
Open the message in a separate window if needed
Click Zoom in the message window and choose a larger percentage
To increase the default reading pane text size, go to View
Select View Settings
Choose Other Settings
Increase the font size for column headings or message list if available
To change compose text size, open a new email
Go to the Format Text tab
Change the font size in the Font group
To increase Outlook interface text size, change your Windows display scaling
Open Windows Settings
Go to System
Select Display
Increase Scale and layout settings