Open Outlook and click on File – Options – Mail – Stationery and Fonts
It will open up Signatures and Stationary dialog, switch to Personal Stationary tab to change default font settings for; New mail messages, Replying or forwarding messages , and Composing and reading plain text message. Here you can also change the generic Theme.
Change Default font styles & settings
For changing default font size, color and family, under New mail message section, click Font.
You will reach Font main dialog, start changing basic font settings; from Font select the font family, under Font style, choose desired style and from Size change the ...