Dude how many emails have you collected? That warning appears and it states that the free version hasn’t been tested with that many emails and I suggest either upgrading to the premium version, or moving off of WP Email Capture (with links to download all your data).
It isn’t a holding your site to hostage btw. Just recommended course of action.
@rhyswynne I just saw this review after reading the description, and I don’t remember reading anything about a limit. What exactly is the limit and are any features disabled when it’s reached?