I am new to ZoHo CRM and am trying to further customize a custom module.  The custom module called Sales Visit includes an Account Field (lookup field), a Contact at Account field (lookup field) and a Contact Email field (Email).  I would like to make sure that the Contact at Account is limited to those contacts actually in that particular account and autopopulate the email field with the Contact at Account's email address.

I've looked into workflow rules and it would seem that functions are needed.  Has anyone already written a function to perform this type automation that would share it?