In Filemaker Pro Advanced 11 ( and 14 ), is it possible to launch the Windows 10 Mail program (WinMail.exe.mui) using the Filemaker "Send event" or some other approach?

You can use Open URL with a 'mailto' link. If Winmail is your default mail app, then it will open up in winmail.

https://en.wikipedia.org/wiki/Mailto

Problem solved with your help.

I am using a global field with a value list (Mail, Outlook, Gmail, Outlook Express) to select the wanted emailer for FMP 11, FMP 14 and FMP16 under Windows XP thru Windows 10.  By setting "Mail" as the default emailer in the Edge browser, I have scripted 'Send Event ["aevt"; "odoc"; "mailto"]' for get "Mail" to open.

Then another script element is "else if'd" for launching "Outlook" with 'Send Event ["aevt"; "odoc"; "outlook.exe"]'.

And yet another "else if" for Gmail with 'Open URL [No dialog; "https://mail.google.com/mail/u/0/#inbox"]'.  However, this only wants to work for Filemaker 11 with "Compatibility" mode unchecked. Do not know why???

And one more "else if", for Windows XP hangers-on, for Outlook Express 'Send Event ["aevt"; "odoc"; "msimn.exe"]'.