I think you are over thinking the process.
However you decide to do it, is fine, the steps that I outlined before are still valid.
really all you are doing is filtering a recordset based on form input and performing an action based on whether the recordset is empty or not. The sample if statements I provided before can be used to accomplish this.
If you have a form with just email address, create a recordset to lookup that email address, if the recordset is empty, the email address was not found, so show the error message.
the only real question is are you filtering the recordset on one from element, 2 or even 3.