MS Outlook 2007 – email view shrunk to unreadable!

Hello – I have MS outlook 2007, which has worked fine for almost a year. However, this morning when I tried to reply to an email, it shrunk the view of the email so tiny, I can’t read it. It does the same with newly generated outgoing emails as well. The font reads calibri 12 pt (I’ve tried changing the font, to no avail), and only changing it to an extreme size – 26 or 32 – makes it readable. But it means the recipient of my emails gets a ridiculously large font! I have changed nothing in the program, and last night, it worked like normal. I have no idea what has happened. Any suggestions?