So long as the filters are only using GET requests to pull down links, there’s nothing fundamentally wrong with them. It’s a basic (though oft-ignored) tenet of web development that GET requests should be idempotent; that is, they shouldn’t somehow change anything important on the server. That’s what POST is for. A lot of people ignore this for convenience’s sake, but this is just one way that you can get bitten. Anyone remember the Google Web Accelerator that came out a while ago, then promptly disappeared? It’d pre-fetch links on a page to speed up things if you clicked them later on. And if one of those links happened to delete something from a blog, or log you out… well, then you begin to see why GET shouldn’t change things. So yes, the perfect solution to this is a 2-step unsubscribe link: the first step takes to you a page with a form on it, and that form then POSTs something back that finalizes the unsubscribe request.

Two step unsubscribe, where the link in the email goes to a webpage with a prominent “click here to unsubscribe” button is often a good thing for unsubscription. It also gives people an option to not unsubscribe, when they click on the wrong link, or hit “return” with the wrong link focused, in a mail inadvertently, which isn’t that unusual in link-laden emails.

Arguably any link that performs such an action via GET is fundamentally broken. A proper unsubscribe should direct to a page with a form that requires a POST submission. (Of course, in the real world, few things are proper.)

You can afford to make a proper PR to upstream.