Sending emails via Books

Sending emails via Books

Anyone else getting similar problems recently ??.....

Hi,

Your message to the following recipient was not delivered. Please find the details below. 

Bounce Details:
Bounced Address :  someone@google.com
Bounce Reason : other ; Status : 5.0.0 (undefined status) ; Daignostic-Code : smtp;542  s omeone@google.com  Rejected ;
Bounced Time : Sep 05, 2017 06:37 PM BST


Regards,
Zoho Team

The email addresses were fine only a few days ago but are now being rejected ?