Funny. I'm somewhat new to the game but my email server has had very few problems delivering anywhere (hosting a small business' email, and personal email for the employees.) I've got spf, dkim, and dmarc. I use tls on everything. Got a static ip (linode) with rdns. I've never had a problem delivering to gmail. For a while i had problems delivering to Hotmail/outlook, but participating in some sort of junk mail reporting program (JMRP i think it was) fixed that issue. Now, if i have deliverability problems, it's cause something broke, or my tls cert expired, or i added a new ip that the email server decided to start using. (Sorry for formatting, on mobile)
Having run my own server for 20 years, my experience is also that it is relatively hassle free. I also run my own DNS and have a static IP, which might help with keeping email related DNS records up-to-date.
Running the server is generally "set and forget". Every few years an issue might pop up that requires attention. These issues are generally due to a tightening of other servers' requirements rather than an actual technical issue. When such things do occur, symptoms are an occasional email rejection, and a bit of digging reveals the cause and fixing the cause returns things to normal. I've never had a wholesale rejection of mail from my server
For example, when SPF and DKIM came in, I had to add those records to my DNS. When Let's Encrypt came on-line I proactively added TLS to the server. A number of years ago lack of a Reverse DNS record got me on a blacklist for a short time. That was fixed by contacting the IP address issuer (my ISP) and getting them to add a reverse DNS record. Just make sure the reverse DNS hostname matches the hostname that your email server uses in its HELO messages. A week or so later I was automatically off the blacklist and the few rejections went away. I've never bothered with DMARC. This is the sum total of my experience with running the server.
At times there have been physical problems with the server or network outages with my ISP, but I discount these on the basis that it is my decision to run a server on a desktop PC in my house rather than in a data centre. Easily fixed if I wanted to throw money at it.
Setting everything up in the first place was a massive pain in the arse, definitely not for the feint hearted (I imagine there are tools/scripts to make it much easier nowadays), but it's been almost plain sailing since.
It's very rare that I have delivery problems, maybe once every year or two, which is roughly the same as through my O365 mailboxes!
Only issue is when there is a delivery problem, there is usually nothing you can do. Some of the block lists have a procedure for removal, many don't.
But after running my own mail server for something like 15 years, I've decided I just don't want the hassle any more (even if it isn't much work), and plan to move everything to O365.
That's been my experience. I've been running a server since 2012. I've had more problem with incoming mail - specifically being unable to whitelist certain Yahoo servers which get killed by SORB and other spam trackers - than with sending email.
I would advice to try with mailinabox.email . It is very opinionated, which, for a beginner, is a good thing with mail.
I'd encourage everyone to try this on a tiny droplet or linode with an unimportant domain (don't just migrate your entire companies' exchange into it on a Friday afternoon). It takes you an hour tops, after which you can poke around and see all the moving parts that make a good mailserver tick.
You'll also be contributing to a stronger, more resilient internet, by making it a tiny bit more decentralized.
