If you’re on the fence about double opt-in, here’s a reason to consider it.

A “spam your enemies” Web site recently sprung up that caused a stir in the email marketing community. The site, SpamZa.com, invited visitors to enter any email address into its Web form and then instantly subscribed the submitted address to hundreds of email newsletters. The intention was to overwhelm recipients with email they didn’t sign up for.

As a result, hundreds of legitimate email marketers could experience unusually high complaint rates and other reputation-related issues. If you use a single opt-in process—that is, people who sign up for your email get automatically added to your list—you could be vulnerable to this tactic.

One way to protect yourself from this and malicious sign-ups in general is to use a double opt-in process—one in which new recipients must respond to a confirmation message before they get added to your list. If you’re not using double opt-in, it may be worthwhile to consider whether switching is an appropriate alternative for your email marketing program. Although it won’t stop malicious sign-ups from occurring, it can help protect the integrity of your list by preventing those unwitting and unwilling recipients and bad addresses from being added.

SpamZa.com was recently shut down but is searching for a new Web host. You can read more on the issue by Laura Atkins on the anti-spam blog Word to the Wise.