As a data point, I have run my own email servers for years. Both professionally (couple million transactional emails per year) and for my personal.
If you follow best practices (which is a pain to setup!), deliver ability is generally on par with other providers, unless you got unlucky and got a bad IP.
Our IP addresses are not on any blacklists, and we don't block SMTP or mail ports.
Tailscale (which we have been using to great effect over the last year or so) provides effectively a 'LAN' where the devices can be anywhere. It provides you with a second interface in the 100.x.x.x range. You can trust that any traffic from that range has been authenticated to connect to your Tailscale network.
Hoppy (as I understand it, I've never used it) is more solving the issue of getting a static IP assigned, with the advantage of it following your device if it moves between networks. You get a second interface that is publicly visible, but can't trust traffic coming in from it.
In fact it'll happen even when you send from gmail to gmail itself!
My deliverability from my own email server to gmail feels better than from my company account (on gmail) to gmail users.
Quick look at my archive, of 37k spams only 7k fails SPF. (I accept all email no matter what.) So it's some signal, but not nearly enough.
It's much easier these days. The ecosystem has gotten more complicated, but the community has put in a lot of effort into automating that complexity away.
I've run a personal mail server for the last 5 or so years and I have SPF, DKIM, DMARC setup correctly, get 10/10 for mail-tester.com and get graded "not spam" for all the other spam tester sites. Spam Assassin loves me and I have a .com mail server.
I can land more or less into personal emails (occasionally I get filtered into spam), but when it comes to corporate emails I pretty much get /dev/nulled each time and can't even land into a spam folder. I can't give out my personal email as a point of contact and have to use my gmail or protonmail instead.
I've all but given up on owning my own email because the protocol has effectively made it impossible to reliably land mail in a mailbox if you don't have a certain amount of outbound mail traffic.
hotmail and icloud are very sensitive and if IP isn't reach a certain reputation(mail volume+age) it's easiser to land on spam even SPF/DKIM/DMARC are passed. But if the recipient interact with sender(mark as non spam, send a reply) then moving forward email send from that won't be flag as spam anymore. So their spam filtering is kind of weak and they used previous interaction as a signal.
gmail, on other hand is rock solid. They have their own false positive obviously but they are rock solid in term of not relying on IP reputation(or less). They are smarte and righfully land your legitimate email on inbox even an email come from a spammy IP.
