How do I know if someone blocked me on iMessage?

There isn’t a reliable way to tell from your iPhone whether someone has blocked you on iMessage.

Things like a missing Delivered status, calls going straight to voicemail, or messages switching behavior can happen for plenty of other reasons too — the other phone may be off, offline, in Focus, or having a network issue.

Apple doesn’t provide a notification or status that confirms you’ve been blocked. So I wouldn’t treat any one symptom as proof.

FAmustafa wrote:

How can I know if someone blocked me on iMessage?

If you get direct or indirect feedback from the recipient, or if you happen to find your messages included as part of a legal proceeding for harassment, you will know you weren’t blocked.

Put differently, if you suspect you are blocked — and given there’s deliberately no feedback to indicate blocking is active — best stop sending. Because you might not actually be blocked.

Ask them. Otherwise, the complete and total lack of responses from them might be a clue.