The days of people running their own servers are gone because of the shortsightedness and laziness of IT managers. They though the "cloud" would be easier and cheaper, and they are now trapped.
I entertained the idea of running my own mail servers for a while. After researching the topic it turned out that the internet now runs on an IP reputation system. Major email services like gmail assume that anything sent from unknown IPs is malicious.
So it looks like we've gotta be well connected to federate with the other email servers now. A nobody like me can't just start up his own mail server at home and expect to deliver email to his family members who use gmail or outlook. So I became a Proton Mail customer instead.
Where sendgrid=any major player, could be Mimecast, proofpoint or anyone else who will forward outgoing email.
Sending reputation is just as applicable if you're using a third party as if you're hosting it yourself, but much less under your control.
The best way to ensure a good reputation is to obtain your own address space from a RIR. Barring that, you need to choose a provider with a decent reputation to delegate the space to you.
There is the slight problem that RIRs ran out of (v4) addresses almost a decade ago.
How does one do that? And what are the costs involved?
Following the links on that page (or performing a simple Google search) leads one to: https://registro.br/tecnologia/numeracao/como-solicitar/
Before I even start this bureaucratic process, I need to create an actual organization. Then I need to be assigned an ASN. Only then I'll be allowed to beg them for IPs. Once all that's taken care of, I need to tell them things like what the IPs will be used for and what my infrastructure is. If they like my answer, then they'll approve my request and finally tell me what the prices are.
I've been through the process about 10 times now at various companies, and the paperwork (at least for ARIN) is no more difficult than what would be expected to justify IP space from your typical ISP. If anything, the ARIN folks are more responsive and technically competent than your average ISP support agent, which makes the process easier.
You have to buy/rent a dedicated IP address (that you'll be able to keep long term), and it warm it up by gradually increasing mail volume over a few months to weeks. But once you have, deliverability shoudl be fine.
I think the bigger issue is needing to keep on top of mainenance of the server.
Are they? I'd bet 90% of the email in your archive went through Google or Microsoft or Yahoo's servers, and most likely a copy still resides there.
If you're sending to or getting a message from a Gmail account, Google still has a copy.
I have arrived at the opinion that what I would do if I moved to selfhost would just be to pay some trivial amount for outbound email via a provider like sendgrid as someone else in these comments has also mentioned. Since I send out maybe a half dozen emails a month I don't think this would be a big deal.
But when I relied on selfhosted email several years ago, I was always inundated with spam, which SpamAssassin was wildly undermatched to handle -- that was one of the main reasons I moved to gmail. So I'm curious what people who are happy self-hosting today are using.
I also run SpamAssassin on my server, but I don't believe it ever had to do anything.