The default font type and size
The default font type and size for Outlook message rows is 8 point Segoe UI, which is displayed like this:
Change the message row font type and size
1. Click the View tab, then click View Settings
2. Click Other Settings...
3. Click Row Font...
4. Change the font or size values are desired. In this example the font size has been changed from 8 point to 10 point.
5. Click OK, then OK, then OK
This has the following result...
