I'm pleased to announce that newer versions of Wine (4.19 and above) now work flawlessly with Winlink Express forms and templates! This means that Winlink Express (RMS Express) is fully functional on Mac and Linux, so ling as you are using a recent version of Wine.
Please note that folks using Crossover (a commercial Wine wrapper) will have to wait until the next update (v20) for this compatibility. For those people, everything expect Forms/Templates will work.
For anyone wishing to get Winlink Express (RMS Express) working on Mac or Linux, here are the instructions: