I know how to change the screen resolution for the entire system. That is not a problem. What I would like to do (for my boss) is to "make everything bigger" in macOS 10.14 Mojave Mail, which is his preferred mail client. I know how to increase the size of the fonts in the mail list and in the massages already. That helps some, but there is also the issue of the left-hand navigation pane (Inbox, Sent, Junk, etc).
Is it possible to increase the resolution of specific apps independently of the rest of the MacOS system? Alternatively, how does one increase the size of other things in Mac Mail?