Error, ERROR_CODE :550, ERROR_CODE :High probability of spam

Error, ERROR_CODE :550, ERROR_CODE :High probability of spam

I have been sending emails to a recipient for years using my Zoho account.  Now when I try to send an email I get the following error:

This message was created automatically by mail delivery software. 
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. 

xxxxxxxx@xxxxxxx.com  Error, ERROR_CODE :550, ERROR_CODE :High probability of spam 


Received:from mail.zoho.com by mx.zohomail.com 
    with SMTP id 1421881016241703.0456711610835; Wed, 21 Jan 2015 14:56:56 -0800 (PST) 
Message-ID:<14b0eb67f82.10fba de51170929.7068166794894656337@zoho.com > 
Date:Wed, 21 Jan 2015 14:56:56 -0800 

Has something changed on the outbound email verification?  How do I fix this such that I can continue to email my supplier?

Thanks, Brian