Set a default font for new email in Outlook 365!: Open File ❯ Options ❯ Mail ❯ scroll down to ‘Compose messages’ and click on the ‘Stationery and Fonts’ button to open the Signatures and Stationery box. In ‘New mail messages’ click Font button and try out the three areas of Font, Font Style and Size. Decide what you prefer (you can also change the colour) – click OK. Do the same for ‘Replying and forwarding messages’ and ‘Composing and reading plain text messages’ then click OK on the main box to save changes