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.