I stumbled upon the TrueDelta website last night. TrueDelta is some kind of alternative to Consumer Reports’ car reliability reports. Anyways, take a look at their enrollment form. In their line of business, it’s crucial to send you periodic emails so that you can take your car repair survey. So they ask you for your email address, plus a backup email address.
Very nice idea if you send mission critical email alerts, what with all the spam filters and email firewalls that are constantly changing their algorithms to block spam. More and more people are getting their emails accidentally blocked, so having a backup email address on file is smart.
One could probably combine this idea with some kind of open or click tracker to automatically send a followup to the alternative address: