Running #chatmail servers is <2h effort per month, according to an ad-hoc poll with 10 operators responding. Some have 10Ks of #deltachat users. Typically 300MB ram is used and max 60gb disc space per server. And all interoperate safely based on high security standards (DKIM and TLS enforced, and only no-metadata #openpgp encrypted messages allowed) .... with typically 0.5 secs end-to-end delivery. Who said again that email is insecure, cumbersome and slow? :)