Verifying E-mail Addresses

[jpratt]

I want to have an option on my e-commerce website where customers can enter in friends' e-mail addresses for an incentive (probably a discount). Essentially, I want to incentivize our tell-a-friend form. Does anybody know of a utility or method to "ping" an e-mail address to make sure that not only the domain exists, but the e-mail account exists on that domain as well?

Additionally, would incentivizing my tell-a-friend form in any way violate CAN-SPAM or have any other negativeethical implications?

I would really appreciate any insight others have on this matter. Thanks.