Unable to send message;Reason:550 5.4.6 Mail rate exceeded limit

Unable to send message;Reason:550 5.4.6 Mail rate exceeded limit

I just bought a subscription user
Why is my account: support@updatedepartment.com = Reason:550 5.4.6 Mail rate exceeded limit
and the other account, notification@updatedepartment.com = [Additional Help: error in body: 554 5.1.8 Sender Address Blocked

Please respond as soon as possible.

Best Regards,

Stanley Nah