It happens to us all on occasions.
What I do is, with that email opened and displayed, press and hold down the CTRL key, then press the + key on the number keypad as many times as you need to make the text readable.
It's a workaround and not a permanent solution.
I would reverse the procedure with CTRL and - (minus key), to return it to normal. I am not sure if enlarging for one email affects all emails or if it is just limited to the one displayed.
Does that help?
Using Outlook, and with my monitor set at its recommended resolution, some of my emails (newsletters, Facebook notifications) are almost impossible to read as the text is too small. View-->Text size makes no difference for these particular emails. Some of the messages have a link which will show it as a web page and I can adjust the size there, but many don't have that link. Short of changing my monitor resolution, what else can I do? My OS is Windows 7. Thanks for any suggestions.