Email is a robust, federated, delay tolerant network. None of the 'solutions' to communications I've seen invented by startups in the last 20 years have captured those properties. Jabber is the closest. Most of the instant messaging clients over the last 20 years have given up enormous value that email brings.
Email servers don't have to be complex. I wrote an SMTP and POP server in a single afternoon in the late 90s. The protocols have lot of optional parts, and if you want to get something quick up and running, there are simple implementations possible. The standard Unix servers are quite complex to administer but that's mostly because they were built for Unix system administrators. I mean, BIND configuration files are also complex, but that doesn't mean we should throw out DNS just because it's not trivially simple to implement.
The only point to reinvent and reimplement everything is if you can make some revolutionary improvement, otherwise, we should just improve what we have.
Email servers don't have to be complex. I wrote an SMTP and POP server in a single afternoon in the late 90s. The protocols have lot of optional parts, and if you want to get something quick up and running, there are simple implementations possible. The standard Unix servers are quite complex to administer but that's mostly because they were built for Unix system administrators. I mean, BIND configuration files are also complex, but that doesn't mean we should throw out DNS just because it's not trivially simple to implement.
The only point to reinvent and reimplement everything is if you can make some revolutionary improvement, otherwise, we should just improve what we have.