That doesn't match my experience of running a mail sever for decades.
The only systems that have had even tiny problems with were Gmail and Microsoft. With Gmail it took a while to build reputation as a non-offender. With Microsoft the first time I sent mail to their way, I got an automated bounce with instructions to forward to a certain address for human verification. That check round took maybe 12 hours and I haven't had any problems since.
I find that pretty reasonable.
But how do you know that when you send mail to a new Gmail contact it won't be silently flagged as spam? And how many times will the recipient have to "un-flag" before the behaviour changeges?
> The only systems that have had even tiny problems with were Gmail and Microsoft
The "only" big provider missing from that list is apple (in the West anyway).
I've never meant to claim that smaller providers that know what they're doing aren't capable of sending proper bounces, setting proper smtp error codes on reception or of handling email to postmaster@.
It's just that with Gmail and outlook not being God net citizens - it becomes unreasonably hard to send legitimate email to a large percentage of Internet users. One possible "fix" is to send mail to Gmail users via a Gmail account and Gmail authenticated smtp servers - and so on for outlook.com - but as the number of "silos" one needs to send data to grows, that solution becomes cumbersome. Not to mention if you publish an mx record for your domain, you should be accepting email... That's the whole point...