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,

One of my users is unable to send messages since yesterday. He is getting message he cannot send.

Error: Unable to send message: Reason 550 5.4.6 mail rate exceeded limit
In Portuguese, as it appears to me:  Não foi possível enviar a mensagem; Razão:500 5.4.6 Taxa de e-mails excedeu o limite.

User Email id: vendas@vivaclima.com.br

Please revert asap.

Luana B.