Mail won't close

i experienced this today after connecting it to gmail. Every time I wanted to close it i had to use force quit. My solution was to stop using it.But I'm curious if there is a more realistic fix.

Force Quit Mail.

Press command + option + esc keys together at the same time.

Wait.

When Force Quit window appears, select Mail if not already.

Press Force Quit button at the bottom of the window.

Wait.

Mail will quit.