Gmail killfiled a domain I was running on a small but reputable ISP I had used since 2001 (there were no spam or reputation issues in 17 years).

They did let one-in-20 or so emails through, but everything else got to gmail recipients’ Spam folder. I wasn’t able to troubleshoot this with Google tools, and there’s no one to talk to at google.

(Worst thing, you get no feedback - except realizing a month later that someone didn’t get an email you sent)

I gave up and replaced small ISP with fastmail.

My bottom line is that, no you can’t really run your own SMTP server anymore unless google, Microsoft and fastmail let you, by virtue of hoisting 90% of your recipients.

Sure, something like that can happen... but it is not like they have an explicit "allow-list" of domains that mail can be received from. These might be the biggest providers but if me and my friend who do not use their services want to communicate, we will always be able to do so without them.

I have many domains that I use to send and receive mails, and I have personally never had these issues.

Now if I did have a gmail account, I suppose I would have to check the spam folder regularly. But I don't have that problem with my server, it affects their users more so than me.