October 30, 2026
SMS Fraud Protection with Exponential Backoff
Auth0 now supports SMS Fraud Protection with Exponential Backoff for Phone Multi-Factor Authentication (MFA) SMS delivery on Enterprise plans.
This feature helps mitigate SMS pumping and toll fraud across outbound phone verification flows.
Why It Matters
SMS toll fraud occurs when malicious actors exploit verification endpoints to generate massive volumes of outbound text messages to premium-rate numbers, leaving organizations with unexpected, exorbitant telecom bills.
Standard static rate limits are often too rigid—failing to effectively stop persistent distributed attacks while accidentally locking out legitimate users who make simple typos. Exponential backoff solves this by introducing dynamic, compounding delays. This drastically disrupts the economics of automated fraud by making sustained attacks slow and cost-prohibitive, while preserving a seamless experience for real users.
Key Capabilities
When enabled, it replaces static rate limits on outbound SMS verification requests with progressive delays:
- Immediate Request Buffer: Permits an initial set of immediate retry attempts to accommodate typos or delivery delays.
- Progressive Wait Times: Increases required wait times between consecutive requests for a user identifier, starting at 1 minute and scaling up to a maximum cooldown of 32 minutes.
- Automatic System Recovery: Decays wait times dynamically as request frequency decreases, resetting limits after extended inactivity to prevent permanent account lockouts.
- Audit Logging: Logs throttled send attempts as
limit_phonetenant log events, including remaining cooldown durations.
Learn more about exponential backoff and how to configure it in our online documentation.











































































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