Email is our work - communication with other humans is the task that still cannot be automated. That's why I am rather sceptical about the productivity boost of "no email days" introduced in some corporations. I suspect they just don't measure the right things.
All this does not mean that we should do all this human communication work in email - only that currently this is the tool most people use. Perhaps we could do this work in a bit more efficient way if we had a more complete toolbox.