All SMS failing to send in eu-west-2 using Amazon SNS

Hello Sean,

SMS delivery has stopped working in the UK.... ?

Although logs show successful message sending, no messages are received on multiple phones, networks (Vodafone, Three, O2), or AWS accounts. Even AWS sandbox verification messages fail to arrive. This likely indicates a carrier issue rather than an AWS problem.

To address the situation:

Contact Carriers: Reach out to Vodafone, Three, and O2 to inquire about potential blocking or filtering of messages from AWS or specific sender IDs.

Check for Regulatory Changes: Investigate any recent changes in UK regulations regarding SMS messaging that might affect delivery.

Review AWS: Verify SNS settings, test different regions, consider alternative SMS providers.

Message Content: Confirm message content adheres to carrier guidelines.

Test Thoroughly: Use a dedicated testing environment.

Regarding the first part of your query: "After 2 years, transactional SMS text messaging suddenly stopped working in UK. All messages in the logs are reported as successfully sent to carrier. To verify this, I tested with 6 mobile phones across three separate networks (Vodafone, Three, O2) - nobody received a message. I also tested it on two separate AWS accounts."

If you have protected your Sender ID with MEF (Mobile Ecosystem Forum), you are required to register your Sender ID through AWS End User Messaging SMS. If you haven't protected your Sender ID with MEF, you can optionally register your Sender ID information through AWS End User Messaging SMS to make future mandated registrations of Sender IDs easier.

Please refer to the United Kingdom registration form: https://docs.aws.amazon.com/sms-voice/latest/userguide/registrations-uk.html

Regarding the second part of your query: "The big clue came when I set up a new AWS account (to setup everything from scratch). While still in sandbox mode, I tried to add several mobile phone numbers as "Sandbox destination phone numbers". None of these numbers received the AWS verification code, even after hitting resend several times."

When you are in the sandbox mode, the monthly SMS spending limit is set to $1.00 (USD). Please check if you have exhausted the spending limit or not.

If you have followed all the above steps and are still facing issues, please refer to the Knowledge Center article below, which provides multiple resolution steps that can be checked. First and foremost, turn on and view Amazon CloudWatch Logs for your SMS messages.

Knowledge Center Article: https://repost.aws/knowledge-center/sns-troubleshoot-sms-message-failures