This article explains how to increase the font size of emails you read in Microsoft Outlook. Instructions apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Microsoft 365.
How to Quickly Change Font Size and Typeface in Microsoft Outlook
Here's how to read email in a larger font in Outlook:
Double-click the message to open it in a separate window.
Go to the Message tab.