FAQ: Why are my SMS messages not being delivered to Sprint or T-Mobile customers?

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Why are my SMS messages not being delivered to Sprint or T-Mobile customers?

The delivery of messages to Sprint and T-Mobile phone numbers is inconsistent. This is not a Klaviyo-specific issue, and it applies only to messages that those carriers consider to be more automated. It is an industry-wide challenge due to Sprint and T-Mobile being more proactive about filtering A2P traffic.

Note that the filtering happens within the Sprint and T-Mobile systems, after the messages have been accepted for delivery by the carrier. As such, the message will show as delivered in Klaviyo. This is a challenge that is shared across SMS messaging providers.

To avoid these carriers blocking your SMS messages to your customers, you can try the following:

  • Make your messages seem more “human”. Use conversational language that will not trigger the blocks.
  • Avoid using many links in your messages.
  • If your customer’s carrier is Sprint, they can text “allow phone number” (ex: allow 5555551000) to the number 9999.
  • If your customer’s carrier is T-Mobile, they can call T-Mobile Support (1 (800) 937-8997 in the US), or they can chat live with support to have your number unblocked.
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