I just upgraded to Snow Leopard and performed a software update to 10.6.1 including Mail 4.1. When I did, I received an “error” stating that incompatible plugins were disabled and to contact the manufacturer for compatible versions.
Is there an update for this?
That message will probably pop up each time you install a new update of Snow Leopard.
If your computer has Core 2 Duo CPU (as opposed to Core Duo), choose Help > Install Add-ons and the Mail plugin will be installed and will work.
If you have a Core Duo CPU, it’s trickier.
I have a Core Duo. If I understood the thread, at this time the Mail Plug-in can’t be used. The next release “should” fix this however?
“will”
I hope I didn’t impugn your programming prowess Annard!! 
I always look forward to the updates!
Cheers.