A client had end up getting ransomware and after it was corrected, they attempted to get back to their contacts via email but when doing so, they noticed that the font size changes in Outlook (it got smaller) when replying or forwarding an email making it difficult respond to statements made by their contacts.
Fortunately, I have seen issue before and remember that the zoom is the culprit. Please keep in mind that Outlook has zoom in a few areas so you will want to check the zoom in the reply window. If replies are in a frame, be sure to click on the Pop Out button.
Correcting the Issue
01. Open Outlook
02. Find an Email
03. Click Reply (Pop Out if necessary)
04. Click on the Zoom button
05. Set Zoom to 100%
06. Hit the OK button to save the change.
You should see the change immediately. Now, close the email and try to reply and forward to see if it is operating normally.
Note: Your Draft folder may need to be flushed after these tests.