how to permanently enlarge type font for hotmail

My hotmail/outlook email has font size set at 10 and every time I type an email I have to raise the font size but if I make an error and have to backspace the font immediately changes back to 10.  I have tried for over a year to find a way to permanently set the font size to a more legible size but have not found anything on the net that works.  Can Microsoft explain in a simple way how I can address this issue with a PERMANENT change or is Microsoft resigning all users of this email to be young or have reading glasses on at all times?