[rsync]

"I'm grateful for the silent block in this case."

That's not the issue - the issue is not alerting the sender that the message has failed.

It's not a big deal if the receiver never receives the message - we can find a different way of reaching out or fix the content problem or whatever. But we never find out. As far as the sender is concerned, the message succeeded.

This is a problem and the very bad spam heuristics employed by even the most competent actors (gmail, for instance) mean that anyone can be impacted by this.