In my case x>10y for a personal server, but that reputation got ruined when some test email account I had created with a weak password and forgotten, got breach

In my case x>10y for a personal server, but that reputation got ruined when some test email account I had created with a weak password and forgotten, got breached and some spammers started sending spam. My mail server (smartermail) notified me within an hour of the abnormal number of emails and I disabled the account immediately. But that was it for the reputation of that IP. Fortunately I could switch to a spare, clean IP. That being said, now I monitor and auto-ban failed authentication attempts to smtp/imap (among others) and running the service is fairly low maintenance. But the morale of the story is that you are only one weak password from one of your users away from your mail server getting blacklisted as a spam server. So while I think it is fairly easy to run a personal server, running one for a small organisation is another matter.