You can roll your own email if you can get your head around setting up an OpenBSD box and configuring OpenSMTPD and the correct domain DNS records - but the issue will be email deliverability. Gmail etc are going to treat as spam most emails that turn up from a residential or VPS linked IP address.
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.
Having hosted a small mail server for friends for over a decade now, I can only think of this as a myth.
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.
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.
In my experience deliverability to gmail is not that hard if you configure stuff correctly. You need a clean IP and domain, rDNS and the usual email stuff like DKIM, DMARC, SPF, but not much else.
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.
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.