PoliteMail Online will work on a Mac, as well as PoliteMail for Microsoft 365, since these are both online. However, PoliteMail for the Desktop requires the Windows desktop version of Office. Microsoft does not support any add-ins for Office for Mac.
It is possible for PoliteMail for the Desktop to be used on a Mac, but indirectly. It would be necessary to set up a Windows Virtual Machine accessed by using Parallels or another product of like kind and quality.