[kh99]

I'm not sure how you'd go about doing that, but I have another idea that might work - put the email address on the url as a parameter, then use a plugin similar to the one for the mod you have installed excpet that the query would check the email address rather than the userid (which it could do without being logged in). It's true that with that scheme anyone who knew a member's email address could unsubscribe them, but that's not really a serious security issue. If you wanted, later you could add something like an automatic PM to the user telling them they'd been unsubscribed, so they could resubscribe if it's a mistake.

If you did implement this, one thing you might want to do is change the plugin code so that it only ever displays one message (like "thank you, you're unsubscribed") even if you're passed an invalid email, that way it couldn't be used to guess at member's emails.