You don't have to stick with the default font when typing your emails - it's easy to change. If you use a Microsoft email account, such as Hotmail or Outlook.com, there are some simple steps you can take to increase the font size so it's always larger by default, for example.
How to change your email font size
Go to outlook.com and log in to your Microsoft email account, such as your Hotmail address, MSN or Live account.
Click on Settings (the cogwheel icon at the top right hand corner) then click on Options.
Click on Mail (top-left corner), then click on Layout then click on Message Format.
You'll be presented with various options for changing your default font size, plus the type of font you use, for when you're typing emails. Click Save and you're done.