How do you open boards that someone shared with you via email?

Just follow these simple steps:

1. Open the email on your iOS device (iPhone or iPad) using Apple's mail app.

NOTE: It is important to use Apple's native app or you may not be able to open the board that was attached in the email.

2. Press on the attachment to download it

3. Press on the attachment again and select the app you want to use to open it (i.e. Bitsboard)

Voila!  You should now be all set.