Associate a Web to Case form with an existing Account or Contact

Associate a Web to Case form with an existing Account or Contact

Cases are associated with Accounts through the Account Look-up field.  When building a case form to publish on the web, how can I architect it such that I associate the incoming Case record with an existing Account or Contact (Account Look-up field not an option to place on the form)?  If I put the email field on the case form, will Zoho CRM match it to an Account/ contact that way?