Why You Still Can't Use This Week's Hottest iPhone App

Mailbox, a highly anticipated email app for iPhone, finally launched yesterday.

But you probably can't use it yet.

Early demand for the app was so high that the company had to create a reservation system to handle all the new users.

If you want to try Mailbox, you have to go to the company's site and register. You'll get a text message with two reservation codes that you need to put in the app after you download it to your iPhone.

Then you'll see a screen like this:

That screen shows how many people reserved a Mailbox spot ahead of you. From there, it's a waiting game.

As of this writing, there are approximately 500,000 people waiting to get access to the app. Mailbox says it will let in more users at an exponential rate.

So, why is it even making you wait in the first place?

Mailbox's servers handle push email, which means you get your message as soon as it arrives. You don't have to open the app and refresh your inbox to look for new messages. That process requires a lot of server power, especially when it's under the kind of demand Mailbox has.

It's a minor annoyance, but Mailbox is doing the smart thing for its users by letting only a few people in at a time. That'll keep the service from crashing and make hundreds of thousands of users very happy once they get to try the app.

What's so great about Mailbox? Click here for our walkthrough of the app >