Outlook font size small/large
Launch Outlook
Start composing a new email message. It doesn’t matter if you choose to compose a new email message or a reply to one of the emails in your inbox.
If you are using Outlook 2007 or Outlook 2016, navigate to the Format Text tab of the ribbon at the top. If you are using Outlook 2010 or Outlook 2013, however, navigate to the Message tab of the ribbon at the top.
Click on Zoom.
In the Zoom dialog box that opens up, select 100% under the Zoom to
Click on OK to save your new zoom settings and close the Zoom dialog box. As soon as the dialog box closes, you will see that your zoom factor has been reset to its default value, turning the illegibly small font that you see when composing email messages back to its default size.