Hi, and thank you for asking your question.
Please open up your email window now, and press CTRL + 0 together, on your keyboard. This should reset back the text size all right.
If you need further assistance with this issue, please reply back using the box below. I'd appreciate it if you could kindly take a moment to submit a positive rating at the top of this page. Thank you :)
Just to clarify, you will need to press the CTRL and the 0 (zero) keys together on your keyboard; do this while on the email window itself. If this works for you, kindly do not forget to rate my service at the top of this page. Thank you!