SMTP Error! Data not accepted. SMTP server error: Relaying disallowed

SMTP Error! Data not accepted. SMTP server error: Relaying disallowed

I am using Joomla 2.5 and a contact form to send contact info by smtp.zoho.com. My email from address is the same as my Zoho email account address. In my Zoho email account I have the Send As listed with my Zoho email account address.
My Joomla smtp settings  - smtp auth: yes, smtp security: ssl, smtp port: 465, smtp username and password: Zoho email account address and password, smtp host: smtp.zoho.com. When I try to submit the form I get the SMTP Error! Data not accepted. SMTP server error: Relaying disallowed. What am I doing wrong?