I selected one of the server and then close the mail window, but there are just so many to go through.
1) The email are seemingly created based on some of my calendar events. Why they tried to send me emails?
2) How can I efficiently close all these windows in one go, instead of making a selection of outgoing server than close a mail window?
I have tried to quit the mail app from its context menu of the Dock, but it just forces one of the mail window to the foreground.