Yep. I work on software that runs on thousands of mail servers (I work on Virtualmin), and it is entirely possible to run your own mail server with good delivery rates. It's honestly not even that hard, if you get SPF, DKIM, PTR records in DNS right, and you correctly handle bounces and unsubscribes promptly. We've been sending out a few thousand emails a day for over a decade without incident, and we have several people who run bigger mailing lists than we do.
Though there are a few minor caveats to this. Microsoft (Hotmail, Outlook, Live, etc. addresses) mail servers are ornery, in that they hold grudges against IP addresses for a long time (seemingly forever, as the server we moved to recently had been in our possession for non-email use for a couple of years, and it was still on a Microsoft blacklist from a prior owner's abuse), and they make you jump through a few hoops to get it removed. Even with SPF and DKIM, they rejected 100% of our mail until we got off of their blacklist. Our previous server never had that problem...but we'd been on the same IP for like five or six years.
You need to be on an IP that is dedicated and that you're going to own for a long time, and not part of consumer IP blocks; you can't effectively run a mail server on a cable or DSL line, even business class, without jumping through a lot of hoops. But, if you're in a colo, you'll be fine. This also applies to AWS and other cloud server IP addresses; as I understand it, huge swaths of them have been burned by spammers who spin up and spam until they get shut down, and then move to another.
So, I guess it's relatively tricky to get things working at the beginning and you may have to fight a little with some of the big email vendors, but it's not really an ongoing thing, in my experience. Get it right, and then don't spam or let your users spam, respond appropriately when abuse does happen, and you can run your own mail server relatively painlessly.
Though there are a few minor caveats to this. Microsoft (Hotmail, Outlook, Live, etc. addresses) mail servers are ornery, in that they hold grudges against IP addresses for a long time (seemingly forever, as the server we moved to recently had been in our possession for non-email use for a couple of years, and it was still on a Microsoft blacklist from a prior owner's abuse), and they make you jump through a few hoops to get it removed. Even with SPF and DKIM, they rejected 100% of our mail until we got off of their blacklist. Our previous server never had that problem...but we'd been on the same IP for like five or six years.
You need to be on an IP that is dedicated and that you're going to own for a long time, and not part of consumer IP blocks; you can't effectively run a mail server on a cable or DSL line, even business class, without jumping through a lot of hoops. But, if you're in a colo, you'll be fine. This also applies to AWS and other cloud server IP addresses; as I understand it, huge swaths of them have been burned by spammers who spin up and spam until they get shut down, and then move to another.
So, I guess it's relatively tricky to get things working at the beginning and you may have to fight a little with some of the big email vendors, but it's not really an ongoing thing, in my experience. Get it right, and then don't spam or let your users spam, respond appropriately when abuse does happen, and you can run your own mail server relatively painlessly.