This assumes you are running a recent version of MacOS (High Sierra 10.13, Mojave 10.14, Catalina 10.15 or higher). Mail will NOT WORK on versions lower than High Sierra 10.13.
If you have Mac Mail (aka Mail.app) connected to Exchange do the following:
click Mail - Preferences
click account corresponding to Canisius Exchange
click Server Settings
change User Name to canisius\username
uncheck Automatically manage connection settings
change the first part of Internal and External URL fromto
REBOOT!!!! This is needed to clear some background processes used by Mail that do not get their settings updated until a reboot is done.