Email account disabled

Dear Sir/Madam,

I am having one very strange problem with one of my email address

Unable to connect SMTP server:smtpout.mail.zoho.com
Reason:Authentication failed:554 5.1.8 Sender Address Blocked

email ID : dipesh@sharpadvertizing.com

just want know, why it has been blocked,
what went wrong?

Regards,
Pramit