Quick take
The goal is not to block every unusual OTP request. The goal is to slow abuse, cap spend, preserve real-user conversion, and give support enough context to understand why a message was not sent.
Practical pumping controls
Layer controls so one weak signal does not punish legitimate users.
| Control | What it limits | Implementation note |
|---|---|---|
| Per-recipient limits | Repeated sends to one number | Track attempts by normalized E.164 number, user, IP, and device. |
| Country controls | Unexpected high-cost or high-risk destinations | Require explicit launch approval for each destination country. |
| Spend limits | Runaway cost exposure | Set daily and hourly caps by app, country, and use case. |
| Resend controls | User-triggered spam and accidental duplicates | Use cooldowns, idempotency keys, and one active code window. |
| Suspicious prefixes | Known high-risk ranges or anomalous routing | Review with provider and avoid hardcoded assumptions without evidence. |
| Support-visible block reasons | Mystery failures | Show safe reason categories without exposing abuse rules to attackers. |
Protect conversion while reducing abuse
A blocked OTP should not strand a legitimate user. Offer safe retry timing, alternative authentication when available, and support escalation for high-value account actions.
Do not expose fraud logic in user-facing copy. Internally, store the control that fired, the confidence level, the destination, and whether the send was skipped or allowed with monitoring.
Keep OTP fraud controls explainable
Notilify connects OTP sending, abuse controls, delivery evidence, and support visibility.