Probably because there simply isn&#x27;t money to be made in being an e-mail startup.<p>Or, more correctly, there isn&#x27;t <i>enough</i> money to be made to satisfy VC investors. Mailbox and the like could have lived quite comfortably as paid-for apps with comfortable but small levels of profit, but that isn&#x27;t what Silicon Valley rewards.<p>EDIT: also, IIRC Apple&#x27;s restrictions on background processing meant that they needed to have every user&#x27;s account set up on their servers to process push notifications. Did that ever change? If not that&#x27;s a non trivial expense&#x2F;complication to scaling, especially when you&#x27;re up against an OS-integrated app that doesn&#x27;t have those restrictions.