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

Hi

I am having problem to send email with this user: erwin@theamericangoldenfoods.com

Unable to send message: Reason 550 5.4.6 mail rate exceeded limit

Is the CEO of the company and I have checked and he does not send more than 20 emails per day, only for clients.

Could you help me please unlock him.

Thanks

Best Regards