We never liked the choices available for secure email for mobile devices, because no email client with PGP encryption was available for smartphones. Instead, we had to install PGP Universal, which is a server-based version of PGP, designed for enterprise environments, which does the PGP encryption and decryption on the server, with PGP private keys stored on the server. Not a good architecture for consumers in today's climate. We strongly preferred to do PGP on the client side, but we were a long way from having a PGP client for mobile devices. And even if we had a PGP client, we would still be stuck with email metadata exposure on the servers, even with the message body encrypted.
That's why we were unhappy with Silent Mail, and why we were discussing a phaseout for some weeks before these events. The Lavabit event made it clear we could not put it off any longer.
--Phil Zimmermann (spelled with two Ns)