Now that there's more info, this is cron attempting to email because the cronjob failed (mover returned error 1)
Mover even if all shares are disabled to move always runs (but, there has to be some share that is eligible to move, otherwise it wouldn't be attempting and failing). Either way, have you remove all email addresses in the smpt settings if you don't want to use it.
Otherwise, you need to set up gmail to accept connections from less secure clients (or whatever it's called in gmail settings)