1. Launch Mailbox. Go to Settings > Dropbox > Add Dropbox Account then link your account. If you already have Dropbox for iOS installed it’s dead easy.
Once your account is successfully connected, Dropbox will inform you of your free space earned:
Normally, referring friends to Dropbox will earn you 500MB for each successful sign up. Linking your Mailbox to Dropbox is by far the fastest and easiest way to earn free storage. Even if you delete Mailbox, the free storage will stay in your account.
Let us know if you’re going to jump on this.
Update: If you previously linked your Dropbox account before this offer, you won’t get the extra space. Unlink then re-link your account to get your 1GB (via @ssklassen19).