I ran my own email server for a while and to be frank, it was a pain in the butt. Even though I spent a lot of time reading up on the proper way to set things up and tried to apply that as well as I was able, there was this lingering feeling that something somewhere was misconfigured, if not from a mail authentication/anti-spam standpoint, then from a network vulnerability one, and of course it needed to be continually maintained with patches, config updates, etc.

Eventually I gave up and moved to Fastmail. The few dollars per month are worth it.

Syncthing on the other hand I found pretty reasonable when I still had need for it, with my only gripe being that the only UI surfaced by several clients is a webpage which feels a bit janky.