> that Google occasionally puts delivered emails in the Spam folder
The thing with gmail is that this is true even even for legitimate email from long-known connections when the path is gmail to gmail!
Even worse, it can be true within a gmail-hosted corporate space, so email from your boss ends up in spam!
So it's nothing specific to whether you host it or not, it's just a reflection on gmail's spam false positive rate being particularly bad.
I'm running an email server for myself since 1998 and in addition some low traffic email servers for a few small companies that I administrate and we have had no delivery problems so far, not even with Google, although I have heard from other people that run their own email servers, that Google occasionally puts delivered emails in the Spam folder.
I always keep an eye if some of our IPs may appear on any of the well known abuse lists, but so far that never has happened. I would guess if once there's coming spam from your mail server IP, it is negatively branded forever.