> I'm obviously being naive about that approach, but I don't remember having trouble reaching Gmail inboxes or those of local providers, and at least for Gmail
There are plenty of those who do have such issues with Gmail.
The simple reason behind all this is that spammers also have near endless patience. If it takes sending 15 emails per day per IP, they'll do it. If it's a criteria you can figure out as a legitimate user, the spammer can as well. They'll "subtract one" and bypass it.
So the end result is that there's intentional fog over the methods. Just things you can try and get right and maybe that's sufficient. Eventually the good side tends to prevail, with some effort. Other than that it's one of the hardest problems out there with insane weight on both sides.
There are plenty of those who do have such issues with Gmail.
The simple reason behind all this is that spammers also have near endless patience. If it takes sending 15 emails per day per IP, they'll do it. If it's a criteria you can figure out as a legitimate user, the spammer can as well. They'll "subtract one" and bypass it.
So the end result is that there's intentional fog over the methods. Just things you can try and get right and maybe that's sufficient. Eventually the good side tends to prevail, with some effort. Other than that it's one of the hardest problems out there with insane weight on both sides.