Outlook 2013 provides the ability to change the size of the text. You might want to make Outlook email text bigger if the text is too small for you to read clearly or you want a larger view to proofread your message with extra care.
Make Font Larger
To make your text larger, choose a larger font size for text in messages you send. For example, select some phrases to make those words bigger for emphasis or increase the size of all text in the message. Press "Ctrl-Shift->" to enlarge selected text. Anyone who views the message as plain text won't see the type in the desired size.
To adjust your view, click the “Zoom” command in the Message ribbon and select a larger percent. This action changes the size of the contents in the messages you compose. To make Outlook email text bigger and easier to proofread, zoom in on specific messages that you want to read and check. To make the text of columns larger, click the “View Settings” command in the View ribbon. Click the “Other Settings” button and click on the “Column Font” button to choose a larger font for columns. Click the “OK” button to save this change.