How to set up GMail with Google Apps for Work so email can only be sent from Zoho?

How to set up GMail with Google Apps for Work so email can only be sent from Zoho?

I want to restrict the sending and receiving by certain email addresses in our domain, hosted with Google, to Zoho Mail. 

I have searched a lot to find a recipe, and it seems that between Google Apps for Work and Zoho CRM it should be possible, but I must be using the wrong search terms.

Does anyone have any experience with this they can share with me please?

Thanks in advance,

Jasper Lawrence
Autoimmune Therapies