I am toying with the idea of whether drip e-mails should offer a chance to opt-out or should I just presume they've opted-in by registering for the website?

Right now I've got the default REW setup which is to have a box to opt-in to the new listings via e-mail for saved searches, but no mention of drip e-mails at the moment.

Anyone done any experiments with this? Do you have opt-in text on your signup page? Do you have opt-out text in your drip e-mails?

Thanks in advance...