You need to validate the request by providing the below confirmation code in Zoho Mail Settings.
Confirmation code : XXXXXXXXXXXXXXXXXXX
To enter the confirmation code in Zoho,follow the steps below:
Login to www.zoho.com/mail
Select Mail Settings >> Email Forwarding/POP/IMAP
Click on the Verify link corresponding to the email address to be validated, in the Email Forwarding section
Provide the Confirmation code in the text box provided
Click Confirm