Hi @Simon Mitchell ,
Agree with Andy, there seems to be no option that could change the font of folder pane in Outlook 2019, for this requirement, we may need to change the display of Systems via changing "Make text bigger" or changing "scale and layout", but they would also affect other programs in Windows.
Then, as a suggestion, in order to get this feature in the future, please kindly vote for this idea in Uservoice, which may increase the priority for our engineers to create a possible option or feature that can be included in the future updates of the program, thanks for your understanding and support.
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