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Anti-flooding system
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Anti-flooding system

The anti-flooding system prevents sending an excessive number of messages to the same destination phone number. It protects end users from unwanted message floods and ensures compliance with carrier policies.

The two mechanisms behave differently: mechanism 1 silently drops the message (returns HTTP 200 OK), while mechanism 2 returns error code 60.

Mechanisms

There are two independent mechanisms, both applied per destination phone number.

Mechanism 1 — Duplicate content rate limit

Blocks messages with the same content sent to the same number via the same provider.

  • Limit: max 2 messages per provider
  • Time window: 1 hour
  • Content matching: the message text is not stored — only its hash is computed and compared (for privacy reasons)
  • API response: HTTP 200 OK — the message is silently dropped, no error is returned

Mechanism 2 — Total volume rate limit

Blocks any message sent to the same number regardless of content.

  • Limit: max 150 messages
  • Time window: 1 hour
  • API response: HTTP 500 {"code": 60, "message": "Anti-flooding error"}

If more than 150 messages are sent to the same destination number within 1 hour, subsequent attempts are blocked until the time window resets.

Sequence diagram

ProviderSMS GatewayYour ApplicationProviderSMS GatewayYour ApplicationMechanism 1 — Duplicate content (same hash, same provider, within 1 hour)Message silently dropped,not forwarded to providerMechanism 2 — Volume limit (>150 messages in 1 hour)Message blocked,error returnedPOST /send (same message, 3rd attempt)HTTP 200 OKPOST /send (101st message)HTTP 500 {"code": 60, "message": "Anti-flooding error"}

Error response

Only mechanism 2 returns an error. The send API returns:

{
  "code": 60,
  "message": "Anti-flooding error",
  "details": null
}

Notes

  • The two mechanisms are independent
  • Only mechanism 2 returns error code 60; mechanism 1 silently drops the message
  • Limits apply per destination phone number, not per sender account
  • There is no way to bypass or reset the limits — wait for the time window to expire
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