Most Microsoft apps use the same font by default. However, if you want to always use a different font in one or all of your desktop 365 apps, you can change the default manually. Although you can't ...

Then, under Compose messages panel, click the Stationery and Fonts button. It lets you change default fonts ... it will apply to all other Microsoft Outlook replies, automatically.

Outlook for iOS and Android will finally let users change fonts, which was the most requested feature from Outlook mobile ...

Microsoft has announced a big change to the Outlook mobile app that gives you more control over your email formatting.