Personal email servers will communicate with each other happily but you need a middleman one for important recipients if you want to be sure it gets into an inbox.
Gmail has specific bulk (!) sender requirements, which to my knowledge don’t include a blanket downranking of residential and „VPS“ IPs (the latter are just datacenter IPs anyways). You need TLS, SPF, DKIM, DNS and reverse DNS entries that align, ideally DMARC and that’s pretty much it.
https://support.google.com/a/answer/81126?hl=en#zippy=%2Creq...
At one point I misconfigured a relay as unauthenticated and we got abused by spammers for a day. We got put on all sorts of blacklists within hours and got our IPs cleared self-service immediately after fixing the issue.
If you just send emails completely unauthenticated, yes they will be blocked.
Also not sure why you would choose OpenBSD and OpenSMTPD unless OpenBSD is your style. For example I run maddy on linux, which is pretty easy to configure.