I’m running into an allocated limitation on the number of emails I can send to users per day. I don’t even understand what that means!
Back in the wild west days of the early Platform launch, you could basically send out as many Notifications and invitations per day as you’d like. This was great from a viral growth perspective, and apps like FunWall and Super Wall shot up into the millions of users range really quickly. The downside was the constant barrage of invites and Notifications that suddenly dropped Facebook’s signal-to-noise ratio down the tubes (Internet tubes, naturally). Facebook responded by imposing a hard cap on the number of invites an app could send out at one time, but crafty developers found ways around it by using a succession of invite screens. Facebook responded again by imposing a hard limit on the number of invites per day, but that was limiting the majority of well-behaved apps to punish the minority of naughty ones.
So, in February 2008, Facebook responded by imposing a sliding scale system, based on how well the things you send out are received. This system, essentially a closed feedback loop, makes a good amount of sense: behave and your users will respond, thereby grading your behavior well and rewarding you with more Notifications that you can send to users who will grade your behavior, etc.
You can find out your app’s allocations by visiting the Allocations tab of the Facebook Insights app at http://www.facebook.com/business/insights/app.php?id=123456&tab=allocations ...