554 5.7.1<n@abc.com>:Recipient address rejected:Policy Rejection-SENDEQUOTA_REJECTION

1 of my user getting this error just after sending emails:
554 5.7.1 n@abc.com: Recipient address rejected: Policy Rejection- --SENDER_QUOTA_REJECTION.
Plz I want to know & how can I recover this?

I am NOT using POP3 & SMTP of my ISP, using dremhost.


How many emails? You only get 100/hr.