My experience with running my own mailservers for the last 20 years: it's definitely not hard. It's not painless, you need to spend a little bit of time now and then, and you need to know a little bit more about email than how to hit "send" in your mail client.
It's annoying that the default settings of almost all mail server software are suboptimal, but once I set it up correctly (yes, that took some time but nowadays there are plenty of tutorials) I had to do almost no maintenance at all. Apart from power failures that were unavoidable, the biggest issue has been spam blocker lists becoming outdated or going out of service. After that, the occasional hickup after a dist-upgrade or moving to a different country. But on average, my mail server is working perfectly fine 364 out of 365.2425 days. And, this is considerably better than the mail servers at the universities and companies I've worked at. Your Gmail might have given you no problems, but it is not working 100% of the time for everyone either.
So I'd say maintaining your own mailserver is as hard as painting rooms yourself, or changing the battery or light bulbs of a car. Not everyone wants to do that, and that's fine. If you're not afraid of it, it's a rewarding experience.
It's annoying that the default settings of almost all mail server software are suboptimal, but once I set it up correctly (yes, that took some time but nowadays there are plenty of tutorials) I had to do almost no maintenance at all. Apart from power failures that were unavoidable, the biggest issue has been spam blocker lists becoming outdated or going out of service. After that, the occasional hickup after a dist-upgrade or moving to a different country. But on average, my mail server is working perfectly fine 364 out of 365.2425 days. And, this is considerably better than the mail servers at the universities and companies I've worked at. Your Gmail might have given you no problems, but it is not working 100% of the time for everyone either.
So I'd say maintaining your own mailserver is as hard as painting rooms yourself, or changing the battery or light bulbs of a car. Not everyone wants to do that, and that's fine. If you're not afraid of it, it's a rewarding experience.