MACOS SONOMA REMOVES SUPPORT FOR MAIL PLUG-INS LIKE MSGFILER

…if you upgrade to Sonoma, MsgFiler will cease to function as-is.

This is your opportunity to email Apple at: mail-app-extensions@apple.com and encourage them to do one of two things:

Enhance the Mailkit framework so developers like myself can get a list of mailboxes and file messages programatically.
Incorporate the functionality of MsgFiler directly in the macOS Mail client itself.