according to that link, you will need to add the following code to line 1 of the page:
where email@example.com is a valid email address for your domain.
also in the Universal Email behavior, you will need to set the From address to use the same firstname.lastname@example.org. you can set the Return address to use the dynamic binding from the form.
in the Email server settings, you will need to check the Send From Address as an Extra parameter option too.