Can I cancel this neverending message move in Mail.app?

A few days ago, I decided to move nearly 80,000 messages from an IMAP server to a Gmail server using Mail.app on Sierra 10.12.1:

This task still hasn't completed.

"Checking for Mail…" comes and goes as one might expect, and normal mail functionality seems to work fine. Connection Doctor shows nothing strange.

However, this task has been going on for days, and moves very slowly—I've left the computer on all night and it only chews through a few thousand, occasionally stopping with an error. If I restart Mail.app (it takes a bit to quit), it eventually comes back up with the same 79,718 messages needing to be moved.

Is there any way to terminate this process? I'm inclined to try another tool at this point, but I'd like Mail.app to stop trying to move these messages.

Two things which come to mind that you could try are:

• pressing the Command + . keys
• pressing the ESC key

Either way you may need to do this a few times and wait for the task to register what you're doing.

Delete the account that you were moving mail to and it will cancel the move.

The problem is likely Gmail. It's not well known, but Gmail throttles paid and free accounts once they move a certain amt of mail in the day. The last time I checked, it was 500 MB of mail -- and then you were throttled for 24 hours.

Maybe things have changed -- but this has been my experience in the past. Want to test it? Disable the Gmail account, and see if the other accounts download more quickly.