Is it possible to send an imessage and not to get delivered or read notifications

If someone receives your text do you sometimes not get a delivered notification or a read notification?

These are the read receipts. You can enable or disable these from Settings>Messages>Send Read Receipts.

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Yes that can happen. I have had messages that do not say delivered. But I also know that if the other party has you blocked, is another way that "Delivered" will not show

Or they have the send receipt/delivered disabled.

It doesn't always show "delivered". As for the "read receipts", that's up to the other person. If you don't see it, they have it off.