Executive promises at the time of an acquisition mean absolutely nothing, their main goal is to reduce break-off risk (both of users and employees) due to change of control.

It's far more likely that he was overly optimistic about Mailbox's chances of success at Dropbox. Founders are notoriously delusional about this kind of thing.

Dropbox wasn't worried about maintaining the small existing Mailbox userbase, they were betting they could grow it by millions of users. When it didn't work, it messed up their plans (and promises).

Never attribute to malice that which is adequately explained by stupidity.

> Never attribute to malice that which is adequately explained by stupidity.

As a CEO I'm not sure which of those two explanations I'd prefer.

Stupidity because people who act in malice are dicks. You can choose to be nice, but it's inevitable you'll be stupid at one point or another.

To be fair, that was 3 years ago. A lot can change in that amount of time.

Yes, they could do a spin-out.