When you open a .EMAIL file type that came as an attachment in Windows Mail, the following error message may be displayed:
However you can save the file locally, rename the file with .EML extension and then open it by double-clicking.
As .EMAIL is an alternate file extension for .EML file type (message/rfc822 format), you can simply create a file association for .EMAIL by duplicating the .EML file association settings.
I’ve created a REG file which associates .EMAIL file type with Windows Mail. Download emailfile-wm.zip, unzip the archive and run the file emailfile.reg.