Mail Outgoing blocked. Reason :Mail rate exceeded limit

Mail Outgoing blocked. Reason :Mail rate exceeded limit

Repeatedly getting the alert below. Since I've only sent 1 or 2 tiny emails in the last few days, it seems likely either my account has been hacked or this is just an error on Zoho's part. Clicking "to unblock" has not made a difference.

Dear User,

Mail Outgoing blocked. Reason :Mail rate exceeded limit

However, we realize that this might have been unintentional. To unblock, please  click here .

Thanks,
Zoho Mail Team