The shift, command, Y didn't work, and when I opened the Console app, and tried the menu command, it didn't work, and I didn't see anything showing up on the Console, relative to Mail.
What I did see on the Console was endless lines like this:
MacKeeper Helper.app/Contents/MacOS/MacKeeper Helper", ...): No such file or directory
Nov 14 11:10:04 stevens-computer com.apple.launchd.peruser.502[106] (com.zeobit.MacKeeper.Helper[40111]): Exited with exit code: 1
Nov 14 11:10:04 stevens-computer com.apple.launchd.peruser.502[106] (com.zeobit.MacKeeper.Helper): Throttling respawn: Will start in 10 seconds
Do you have any idea why it keeps doing this, despite my not having MacKeeper on my computer? Could there be a hidden file I can't find? And do you know what "Throttling respawn" means?