By dropping silently I meant really litteraly. If you answer to SMTP commands, you are not silent. You essentially say a spammer server that you are a valid target and that they can go on.
It's not even a question if spammer buy domains to spam.
It's well known and the reason why commercial products provides a feature to filter too fresh domains.
There are procedures to "warm-up" an IP if you are a large provider and if you don't do it and attempt to send a lot of mails to Gmail this will not work. It's not just about DNS records. You could have donne everything perfectly DNS wise and still be blocked by Gmail servers.
You should take a look at the requirements of Gmail for large providers. As far as I recall Gmail does check FcrDNS since last month. On top of more requirements for authentication.
Still you can't just buy an IP, a server, set MX, SPF, DKIM, DMARC, ARC?, FcrDNS and expect large amounts of mail to go through right away.
And again, any communication method will have a spam problem
The major issue here is that anybody can send any email to whoever. Most communication apps won't let you do that certainly not like emails.
You can't open WhatsApp and start spamming the whole world.
You basically can only do that with phone calls and emails ?
So no, SMTP/IMF has rotten foundations. No matter how many (optional) protocol you add on top, it will always be such an hassle to maintain and there will be always people who can't afford that much effort.
Small businesses having to set that up just to reach Gmail is a big problem that they usually externalize with Outlook365 and so on.
Again, Gmail calls the shots because they are the leader. But on paper my fully unauthenticated mail from Barack.obama is perfectly RFC compliant and legit. These protocols that are essential are optional at the end of the day. They became virtually mandatory because of the spam issue and Gmail pushing in the (right) direction because they have leverage.