As someone who runs multiple email servers, this is exactly how it works.

Some email providers will randomly or purposely block emails I sent to them. I get arbitrary blocks or dropped emails on sent emails.

Smaller domains are blocked all the time, ask your local email admin.... just because you're not getting messages about it doesn't mean it doesn't happen

I think others are noting how it can be like this. In my experience:

• My kids' school accounts can only send emails to and receive emails from their teachers' email addresses. All other emails, including those from fellow students, are blocked.
• I frequently have issues with whitelisted email addresses at work. They sometimes are blocked and I have to go through the tedious whitelisting process all over again.