SMS delivery re-tried on repeat every ten minutes to Japanese mobile number (Amazon Pinpoint)

We ran into a similar issue before, and I totally get how confusing this can be.

Amazon Pinpoint does not automatically retry SMS messages every 10 minutes. So if you’re seeing repeated sends for a Japanese phone number (or any number), there’s likely something in your app or workflow that’s causing the message to be re-sent, even if it’s unintentional.Amazon Pinpoint does not retry messages on its own like that. It attempts delivery once per message.

The status = UNKNOWN means Pinpoint did not receive a final delivery status from the carrier. This can happen with certain international carriers, including Japan. It doesn't mean the message failed; it just means the delivery status never came back to AWS.

Many apps or background jobs interpret UNKNOWN as “try again,” and if there’s no deduplication logic, you might end up sending the same message over and over, which sounds like what’s happening in your case.

You can try like updating the logic: Track message_id per recipient/message pair. This way, even if status is UNKNOWN, you’ll know whether a message was already attempted. Don’t retry unless status is explicitly FAILED. Treat UNKNOWN as “wait and monitor,” not “send again.”