Here was a fun thing to work on: subscriber filters.

This is my favorite brand of Buttondown feature: solve an obvious problem with established interfaces.  As of now, you can answer a handful of important and pertinent questions with a mere two clicks:

1. Who has unsubscribed from my newsletter? (Okay, you could have answered this one for a while, but now it's in a more semantically relevant part of the interface.)
2. Who has subscribed to my newsletter that Buttondown has deemed is kinda spammy? (The obvious followup question to this is: "well if you thought they were spammy, why would you let them subscribe in the first place?", to which the answer is: "we don't, but sometimes you may import a spammy subscriber or an email address reveals itself later to be spammy")
3. What subscribers have bounced from my newsletter? ("bounced" is email-speak for "we tried to send them an email and couldn't, so we won't try in the future.")
4. Which subscribers haven't opened my emails in a while? (The cutoff here is fairly arbitrary — three emails — and I might expand it in the future.)

That's it!  Test it out.  Is there a filter you're dying for that doesn't exist? Send me an email and let me know.