There are two key requirements for anything that would actually supplant email: 1. Call the protocol "Email 2" 2. Build something that actually justifies the

There are two key requirements for anything that would actually supplant email: 1. Call the protocol "Email 2" 2. Build something that actually justifies the name I'm only half joking; the messaging around the protocol is almost as important as the protocol itself. iMessage is a good example of how to expose something like "Email 2" to the end user: as a seamless upgrade, indicated by a subtle UI element, when a client happens to negotiate the upgraded protocol with the server. Enabling incremental upgrades to infrastructure is critical, but strict backward-compatibility isn't necessarily so. As long as the architecture of the new protocol makes falling back to IMAP/SMTP straightforward when an upgraded client or server isn't available, Email 2 doesn't have to be able to talk directly to legacy. There's certainly a chicken-and-egg problem in driving enough server adoption to get client vendors to add support while driving enough client adoption to get server operators on board, but there's probably a sweet spot between making a clean enough break with legacy tech that it's more straightforward to implement, while making it conceptually similar enough that it can still plug into the same patterns.