Existing mail viewer window doesn't open when I click on Mail App dock icon I have minimised a mail viewer window to the dock. When I click the Mail icon (to the left of the dividing line) it does not bring the viewer window up. I have to click on the actual viewer window (to the right of the line) to see the window and mail messages. This is new, reverts to normal if I close mail and restart, but soon reverts. Any suggestions please?
I had this problem but it went away when I removed mail from the dock and then docked it again.

Right click icon, select options, uncheck "Keep in Dock"

Right click icon, select quit

Then start mail from Finder>Applications and recheck "Keep in Dock" from the icon that reappears in the dock