BBSmart Email Viewer: a UI-stack trick made BlackBerry's top-selling app

In the mid-2000s BlackBerry was the business email device, yet its native email client could not render HTML messages and would choke, spitting out tag soup. There were no APIs for building an alternative email client and none for substituting a core app the way Android later allowed. Sainsbury, a young developer at his company BBSmart, decided the problem was worth a hack.

The first trick was a listener. BBSmart registered for email-open events on the mail session, and when the user opened a message the handler used the global UiApplication reference to reach the current UI stack. It then pushed its own screen, an HTMLField showing cleaned-up formatted email, directly on top of the native display screen, which stayed open in the background. Closing the email popped both screens, so the swap was invisible to the user.

The second trick kept every native function. Reply, attachments and jumping between unread emails had no public APIs, so BBSmart reached back into the hidden native screen, pulled out its menu, found the matching menu item by name, and invoked it. From the user's perspective BBSmart Email Viewer was a seamless in-place replacement of the built-in mail client that also rendered HTML email properly.

Released in 2007 and sold through fragmented channels like MobiHand, Handango and carrier webstores, the app went straight to the top of the best-seller lists and stayed there for one to two years. It produced several enterprise license purchases above 10,000 seats and one mass US-carrier deployment, and it made Sainsbury a known name in the small BlackBerry developer world.