"You can’t charge a fee, require the recipient to give you any personally identifying information beyond an email address, or make the recipient take any step other than sending a reply email or visiting a single page on an Internet website as a condition for honoring an opt-out request"
(My company provides email delivery software and consulting.)
From: http://www.business.ftc.gov/documents/bus61-can-spam-act-com...
"You can’t charge a fee, require the recipient to give you any personally identifying information beyond an email address, or make the recipient take any step other than sending a reply email or visiting a single page on an Internet website as a condition for honoring an opt-out request"
(My company provides email delivery software and consulting.)
[edit for typo]