I think it's fair game. However, instead of building a feature and then pitching it directly to the user, I would create a landing page for it. Something clea

I think it's fair game. However, instead of building a feature and then pitching it directly to the user, I would create a landing page for it. Something clearly laid out e.g. "(big text) Having Problems with X? -> describe the pain-point feature -> describe the app -> pricing / call to action" This is better for a few reasons, I think: 1) It's less in-your-face. You don't want to be a sales douchebag and make the customer feel obligated to use your app because you've solved a competitor's pain-point. So instead of direct emailing them the pitch, you say "hey our app solves this problem - here's a page explaining why." 2) It's scalable, since you can just send other people to the same page without having to pitch them all the time. You could even set up some adwords campaigns for the specific phrase "XYZ app with ABC feature" and see what happens. You never know - people might be googling for a solution. 3) It's less creepy as it implies that the feature was built for the benefit of everyone (which it was) rather than the few customers that you've stalked :)