I ask my customer to enter their email into the form.

How to make the email that my staff receive show that customer's address instead of a custom address?

In the textfield element that you collect the user's Email address in, click on the Advanced tab. Check the "Mailback as Sender" option and that will send the Email using the user's Email address. (The "Mailback" checkbox, when checked, will send a copy of the Email to the user.)

I checked the Mailback as Sender option but it's still using Joomla's email as sender. Did I miss something? Please help.

AL