tl;dr: If you set up an email server. You just send a few emails to gmail, etc. and you'll know if they are accepted or not. If yes you are set, if not you investigate the problem, maybe really try another IP and eventually fix the issue. It's not like all of a sudden your email becomes undeliverable, unless you start sending spam. Imagine what it would mean for all the people using the email address of a small ISP, some university, etc.

Sorry, but that's FUDish. The reality is if you do a proper email setup (DKIM, Reverse IP, etc.) you will be fine.

If you happen to actually get an IP that somewhat recently happened to be an email server, that was also sent out spam, which isn't something that's likely at all then you'll notice very quickly (just send an email to to gmail, etc.) and what you'll do then is tell your hosting provider you'd like another IP address, because it's not fit for your purposes.

I've been running, moving, switching IPs, providers, domains since 2005 and still am and there is just SO MUCH FUD. It's not hard. It's a one time thing. Personally I never ran into IP reputation issues ever. These are email addresses used in a professional capacity (B2B, communication with governments, etc.) as well as private use ones.

Pretty much every ISP, every university, etc. runs their own email server. Many companies do. Many private people do.

I have run them on the side for those 20 years now, partly as a hobby and so far the uptime was higher than Gmail's and since I use them for private, professional and sometimes for government communication I am dogfooding it and I would have very much noticed if anything bounced.

I have gotten bounces when a setup was initially broken, like when I do something like sending a test email to Gmail and that was off.

The reality is that IP and domain reputation aren't really great ways to filter spam anyways. Yes, it adds, but what makes you think that nobody sends emails from Gmail, a university or other stuff? What makes you think that spammers use static domains, etc.

Heck, not even DKIM and SPF are any guarantee. People will spam you from servers with extremely good reputation. Looking at my spam box most of them are from situations where accounts obviously simply haven't been blocked yet.

No serious spam filtering is done with IPs or domains being an "all or nothing" thing.

Also it's a two-way street. If a user of some email provider doesn't get their email and it becomes known people will be wary of it. And nobody expects the email landscape to stay static. There are newsletter and transactional email services all over the place, lots of marketing platforms running their own email servers and so on.

It's not like everyone does something magic, nor does everyone have connections, money or time to talk to all these companies. An email service not accepting emails won't exist for long.

And something that's also important to realize: If you do start using a transactional email service they oftentimes will make you pay EXTRA for a custom IP so you DO NOT share it with others, so you get BETTER reputation than the cheap one. And you configure your own domain with it. So why wouldn't these emails get delivered? And many of those don't run their own data centers and not all of them have their own IP blocks (though some have).

It's just if you couldn't even do regular private emailing, emails would not be the thing every website uses for login and communication.