In the user settings, I have several Cloudflare instances on my blocklist (e.g. Lemmy.World). When a user from one of those instances DMs me, the sender is falsely led to believe the msg was delivered and the recipient has no way of knowing. It has a nasty side effect comparable to shadow banning.

I have not actually tested this myself. I just know that I do not recall receiving a DM from a user on an instance that I block. But the linked comment is from @wolfyvegan@slrpnk.net who discovered the bug and tested this.