SMS Pumping Solutions: 8 Protection Tools Compared (2026)
Compare the tools and strategies that can detect and block SMS pumping before fraudulent verification requests turn into messaging costs.
Rowan Haddad
Content & SEO Manager
Summary
SMS pumping works by automating requests to a verification endpoint to trigger SMS sends to premium-rate numbers the attacker controls. The most important question is whether your system can block suspicious traffic before the SMS is sent. This guide compares the main approaches available in 2026 from purpose-built verification APIs to provider-agnostic risk scoring and infrastructure-level filtering, covering what each does, who it's best for, and its limitations.
Nearly 1 in 8 SMS verification requests was fraudulent in Prelude's 2025 dataset. Prelude analyzed more than 205 million authentication requests processed through its verification platform and identified 11.83% as fraudulent, representing 24.3 million blocked requests and an estimated $3.26 million in prevented SMS costs.
The attack can remain invisible until the invoice arrives or spend and traffic anomalies become obvious.
SMS pumping, also called artificially inflated traffic (AIT) or SMS toll fraud, works by automating requests to an OTP or verification endpoint. Those requests trigger SMS messages to premium-rate or otherwise high-cost numbers controlled by the attacker. The business pays for the messages; the attacker monetizes the resulting telecom traffic.
SMS pumping is also on the radar of telecom standards bodies. In February 2026, the International Telecommunication Union approved Recommendation E.371, which covers traffic that telecom operators treat as illegitimate, including traffic sent to premium-rate numbers (ITU-T E.371, 2026).
The attack has also become harder to detect with simple IP-based controls. Prelude's 2025 dataset found that residential proxy networks became the dominant attack infrastructure in its analyzed traffic, allowing attackers to distribute requests across large pools of apparently legitimate IP addresses.
The practical question in 2026 is therefore not whether you have rate limiting. It is whether you can make a reliable fraud decision before an SMS is sent.
This guide compares the main SMS pumping protection approaches available in 2026, from purpose-built verification APIs to provider-level filtering, phone-number intelligence, and application controls.
For how the attack works and the signals that expose it, see our guide on how to detect and prevent SMS pumping fraud.
What Separates Effective SMS Pumping Protection From Weak Protection?
The most important distinction is when the fraud decision happens.
Post-hoc detection identifies suspicious traffic after messages have already been sent. By then, the business has usually already incurred the messaging cost.
Pre-send protection evaluates the verification request before dispatch. If the request is blocked or routed to a non-SMS challenge before dispatch, the fraudulent SMS never reaches the carrier.
Six capabilities matter most:
Pre-send risk assessment. The system evaluates the request before SMS dispatch and can block or challenge high-risk traffic. If blocking happens after the SMS is sent, you've already paid for it.
Phone-number and telecom intelligence. Useful signals include number type, carrier, risky prefixes, premium-rate destinations, and historical reputation. These signals can be more useful than IP blocking alone, especially as residential proxies make IP-based controls less effective.
Velocity and behavioral detection. Sequential number ranges, bursts of requests, unusual country concentrations, poor verification conversion, and abnormal destination activity are common attack signals. Strong solutions surface these automatically.
Fallback handling. When a high-risk request is blocked, can your flow route to a different channel or prompt a step-up challenge? Blocking without fallback can create friction for legitimate users caught by overly aggressive filters.
Network-level intelligence. Providers that see traffic across many customers can identify coordinated attacks that would be difficult for an individual application to detect from its own traffic alone.
Actionable enforcement. A risk score is only useful if the system can turn it into an action before the SMS is sent: block, challenge, route to another channel, or apply additional verification.
Purpose-Built Verification Fraud Tools
These products combine OTP delivery with fraud controls. They are generally the lowest-effort option for teams building or rebuilding a phone-verification flow.
Prelude Verify API
Prelude's Verify API evaluates verification requests for fraud before sending the code. Suspicious requests can return a blocked status without sending an SMS. Prelude can also return a challenged state that routes suspicious requests through non-SMS and non-voice channels when that capability is enabled.
Its fraud detection combines telecom, behavioral, device, network, and historical signals. Prelude recommends sending additional signals including IP address, device ID, device platform, and device model to improve detection accuracy. These can be collected automatically via Prelude's frontend SDKs or passed from the backend.
Prelude's 2025 dataset found that 11.83% of analyzed authentication traffic was fraudulent, with Prelude successfully blocking 24.3 million fraudulent requests and preventing an estimated $3.26 million in SMS costs.
Verify also handles routing and fallback across multiple providers and channels, so fraud prevention can be part of the same verification infrastructure rather than a separate scoring API.
Best for: Teams building phone verification who want fraud prevention, routing, fallback, and verification analytics in one integration.
Limitation: Stronger fraud prevention benefits from additional signals such as IP address and device information. Teams need to collect and pass those signals, either directly or through Prelude's frontend SDKs, which is additional implementation work beyond a basic API integration.
Infobip Signals
Infobip Signals is designed specifically to detect artificially generated OTP traffic. It uses machine learning and adaptive learning algorithms to analyze signals including phone-number behavior, number ranges, phone-number types, message frequency, and error patterns.
Signals calculates a risk assessment for messages and can automatically block destinations or number ranges that exceed configured thresholds. Infobip says blocked traffic is not charged and does not count toward monthly volumes.
Best for: Teams already using Infobip for authentication who want automated AIT detection without building a separate fraud layer.
Limitation: Signals is part of the Infobip ecosystem. It is not a provider-agnostic scoring API that can be placed in front of another SMS provider.
Twilio Verify Fraud Guard
Twilio's Verify Fraud Guard blocks suspicious messages from being sent by a Verify Service. When it detects SMS pumping or unusual destination traffic, it blocks the destination prefix of the suspected fraud. It offers three protection levels: Basic, Standard, and Max, with Standard as the default. Twilio cites false-positive rates under 1% for Standard and under 2% for Max. Fraud Guard is part of Twilio Verify rather than a separate fraud API, and is turned on or off per Verify Service.
Fraud Guard protects only the SMS channel and uses behavioral and traffic signals to identify suspicious verification activity.
For teams using Twilio Programmable Messaging rather than Verify, Twilio offers a separate SMS Pumping Protection feature. Twilio provides it at no additional cost in the US and Canada. For other countries, pricing is listed on each country's SMS pricing page.
Best for: Teams already using Twilio Verify who want built-in SMS pumping protection without adding another provider.
Limitation: Verify Fraud Guard is part of Twilio Verify. Programmable Messaging customers use the separate SMS Pumping Protection feature.
Provider-Agnostic Risk Scoring
A different approach is to keep your existing SMS provider and insert a risk decision before the SMS send. This is useful when migrating providers would be expensive or disruptive.
Twilio Lookup SMS Pumping Risk Score
Twilio's Lookup API provides a dedicated SMS Pumping Risk Score that can be used regardless of which provider actually sends the SMS. The score uses Twilio's proprietary risk model and incorporates signals associated with SMS pumping activity.
Twilio returns a numeric SMS Pumping Risk Score from 0 to 100, with higher values indicating greater risk. Its documentation provides recommended ranges labeled Low, Mild, Moderate, and High. Your application can use the result to decide whether to send the message, add friction, or block the request. Twilio provides guidance for interpreting the score, but the enforcement policy remains under the customer's control.
The score is account-specific: it is based only on traffic Twilio sees on your account, not other customers' traffic. Twilio recommends querying the API before each user-generated OTP request rather than caching results, because the assessment can change as traffic patterns change. Twilio does not recommend using SMS Pumping Risk Score for US or Canadian phone numbers.
Best for: Teams that want a provider-agnostic SMS pumping signal without replacing their existing SMS infrastructure.
Limitation: Lookup provides the risk assessment; your application implements the enforcement logic. Each lookup also adds a separate API request and associated cost.
Telesign Intelligence
Telesign Intelligence provides a real-time risk recommendation that you can use to allow, flag, or block a number, along with reason codes. Its signals include phone type, carrier, IP and device data, and behavior patterns such as anomalous traffic and usage velocity. Telesign also positions its platform for detecting IRSF and other telecom fraud.
A useful characteristic is explainability. Rather than returning only a generic risk score, Telesign provides reason codes alongside the assessment, which can feed into an existing fraud engine.
Best for: Teams that need provider-agnostic phone intelligence and want detailed reason codes alongside a risk score.
Limitation: It is a scoring layer, not a complete verification flow. Your application implements the allow, challenge, or block decision, and each lookup adds an API call and some latency.
Messaging Infrastructure-Level Protection
Infrastructure-level controls are useful when your SMS provider already has visibility into the traffic being sent through its network.
AWS End User Messaging SMS Protect
AWS End User Messaging SMS Protect provides country-level controls and AIT risk filtering. Within a Protect configuration, each destination country can be configured as Allow, Block, Monitor, or Filter.
Monitor mode allows messages while reporting AIT risk. Filter mode uses AWS's AIT detection model to identify and block messages considered high risk.
Monitor and Filter modes incur additional charges for AIT risk evaluation. AWS also states that its statistical models do not guarantee complete protection and recommends additional application-level safeguards.
In Monitor mode, AWS adds its blocking recommendation to metrics and events, so teams can see what would be flagged before switching to Filter.
Best for: Teams already sending SMS through AWS that want a provider-level AIT filtering layer.
Limitation: SMS Protect is not a substitute for application-level fraud controls. Monitor and Filter modes add evaluation charges, and AWS recommends supplementing them with application safeguards.
Telnyx Verify API
Telnyx provides Verify for SMS and voice authentication, alongside Number Lookup for carrier and phone-number information.
Telnyx's fraud prevention guidance recommends rate limits per IP, phone number and user, restricting SMS to approved countries, and tracking the ratio of codes sent to codes verified. It flags sequential numbers, high-risk country codes, volume spikes and a verification conversion rate below 20% as possible signs of an attack.
Best for: Teams using Telnyx that want phone-number intelligence and flexible application-level controls around their verification flow.
Limitation: Number Lookup and the Verify API are not a complete fraud system by themselves. Effective SMS pumping prevention on Telnyx requires application-level fraud controls.
Google Cloud reCAPTCHA SMS Defense
Google's reCAPTCHA SMS Defense provides a risk score before an SMS is sent. Scores range from 0.0 to 1.0, with 0.0 indicating low confidence that SMS toll fraud is occurring and 1.0 indicating high confidence. Applications can use the assessment to allow or block an SMS before it is sent to the SMS provider.
The standalone reCAPTCHA SMS Defense capability is generally available (GA). Google announced its GA release on February 20, 2025.
For Firebase Authentication and Identity Platform, Google provides an integrated SMS Defense workflow that automatically assesses SMS authentication requests. The integration compares the risk score against a configured threshold and can prevent the SMS from being sent when the assessment exceeds that threshold.
This specific Firebase Authentication and Identity Platform integration is currently Preview (Pre-GA) and is subject to Google's Pre-GA Offerings Terms.
The integration supports two enforcement modes. In Audit mode, a failed toll-fraud assessment can trigger fallback verification methods rather than blocking the authentication flow. In Enforce mode, a failed assessment blocks the request and the SMS verification code is not sent. Google recommends starting in Audit mode to validate the configuration and monitor results before enabling enforcement.
Best for: Teams already using Firebase Authentication or Identity Platform that want native SMS toll-fraud protection with minimal additional application infrastructure.
Limitation: The Firebase Authentication and Identity Platform integration is currently Pre-GA. Teams using other authentication stacks can integrate SMS Defense directly through the reCAPTCHA API.
Baseline Application Controls
Dedicated fraud products are not a reason to skip basic application controls. These defenses are inexpensive, reduce attack volume, and give specialized detection systems fewer requests to evaluate.
Rate limits per phone number, IP, session and account. IP limits alone are no longer enough, because attackers spread requests across residential proxy networks.
Country and destination controls. Don't send verification SMS to countries you don't serve.
CAPTCHA on suspicious requests, as an extra layer rather than a primary defense.
Application context before a send, such as a session or account step, so an unauthenticated endpoint can't generate unlimited OTPs.
Conversion monitoring. A falling send-to-verify rate often shows an attack before send volume does.
For how to set these up, see how to stop SMS pumping on your signup form. For the warning signs to monitor, see how to detect SMS pumping fraud.
How the Approaches Compare
Approach | Pre-send enforcement | Phone / telecom intelligence | Provider-agnostic | Primary tradeoff |
Prelude Verify | Yes — block or challenge | Telecom, behavioral, device, network and historical signals. | No | Requires adopting Prelude for verification |
Infobip Signals | Yes | Number, range, type, behavioral signals | No | Requires Infobip |
Twilio Verify Fraud Guard | Yes | Destination traffic patterns | No | Requires Twilio Verify |
Twilio Lookup SMS Pumping Risk Score | Decision support; you enforce | SMS pumping-specific risk score | Yes | You build the enforcement logic |
AWS SMS Protect | Yes, at messaging layer | AIT risk model | No | Monitor/Filter modes add evaluation charges |
Telnyx Verify + Lookup | Partial / application-controlled | Carrier and line-type intelligence | No | Application-level fraud controls remain your responsibility |
Telesign Intelligence | Scoring; you enforce | Phone and fraud intelligence | Yes | Separate lookup and decision layer |
Google reCAPTCHA SMS Defense | Yes; Firebase/Identity Platform enforcement is Pre-GA | SMS toll-fraud risk signals | Via reCAPTCHA API | Standalone SMS Defense is GA; Firebase/Identity Platform integration is Pre-GA |
Baseline controls | Partial | Limited | Yes | Not sufficient alone against sophisticated attacks |
Choosing the Right Approach for Your Stack
If you're already on Prelude: Verify's fraud prevention is built in. Pass the recommended IP and device signals for stronger detection, and keep application-level rate limits and destination controls as additional layers.
If you're choosing a verification provider from scratch: Evaluate the fraud system as part of the verification product. Prelude Verify, Infobip Signals, and Twilio Verify all put fraud controls directly into the verification flow.
If you're on Twilio Verify: Fraud Guard is built in and offers Basic, Standard, and Max protection levels. Tune the level to your risk tolerance.
If you're on Twilio Programmable Messaging: Enable SMS Pumping Protection. If you need a provider-independent risk decision, consider Twilio's Lookup SMS Pumping Risk Score.
If you're on Infobip: Signals is the natural first layer. It is integrated with the Infobip messaging platform and can automatically block high-risk destinations and ranges.
If you're on AWS: Use SMS Protect for infrastructure-level AIT filtering, and keep application-level rate limiting, destination controls, and anomaly detection in place alongside it. AWS explicitly recommends additional application safeguards.
If you're on Telnyx: Use destination controls and Number Lookup, then implement the rate-limiting and anomaly-detection controls recommended in Telnyx's security guidance.
If you need a provider-agnostic layer: Twilio Lookup SMS Pumping Risk Score and Telesign Intelligence are both worth evaluating. Twilio's score is more narrowly focused on SMS pumping; Telesign provides broader phone and fraud intelligence with detailed reason codes.
If you're already on Firebase or Google Cloud: reCAPTCHA SMS Defense is GA as a standalone capability. The Firebase Authentication and Identity Platform integration is currently Preview (Pre-GA), so evaluate its launch stage accordingly for production use.
If you're early stage: Start with rate limiting, destination controls, spend alerts, and basic anomaly monitoring. Add pre-send fraud intelligence before SMS volume becomes large enough for a single attack to create a material financial loss.
FAQs
Do I need to switch SMS providers to get SMS pumping protection?
Not necessarily. Provider-agnostic options such as Twilio's Lookup SMS Pumping Risk Score and Telesign Intelligence can sit alongside an existing SMS provider, while application controls such as rate limiting and destination allowlists work independently of your provider. Switching providers can still make sense if you are starting from scratch or if your existing provider's fraud controls are insufficient. Purpose-built verification APIs can reduce the amount of fraud infrastructure you need to build and maintain yourself.
What is the difference between pre-send blocking and post-hoc detection?
Pre-send blocking evaluates each request before an SMS is dispatched. If a request is flagged as high-risk, no message is sent and no carrier cost is incurred. Post-hoc detection identifies fraudulent traffic after messages have already been sent, typically through billing anomaly alerts or dashboard reports. The practical difference is who absorbs the cost: pre-send blocking means fraudulent requests generate no charge; post-hoc detection means you've already paid for every fraudulent message before you knew it was fraudulent.
Will SMS pumping protection block legitimate users?
Yes, false positives are possible. The risk varies by product, configuration, traffic mix, and enforcement threshold. Most of the tools in this guide look at signals tied to SMS pumping, such as number ranges, number types, destinations and request velocity, rather than relying only on broad geographic blocks. The risk of false positives increases when teams use blunt controls like full country bans without phone number intelligence to distinguish real users from bots within those markets. Using layered signals rather than single-factor blocking can help reduce false positives.
Is CAPTCHA enough to stop SMS pumping?
No. CAPTCHA can make automated abuse more expensive and can filter low-effort bots, but it does not address the underlying telecom fraud signals that drive SMS pumping. Use CAPTCHA as one layer alongside rate limiting, destination controls, behavioral detection, and pre-send phone-number or network intelligence.
How do I choose between built-in verification fraud protection and a provider-agnostic scoring layer?
The main tradeoff is integration effort versus flexibility. Verification APIs with built-in fraud protection, such as Prelude Verify, Infobip Signals, and Twilio Verify Fraud Guard, apply it inside the API you're already calling, so there is no separate enforcement logic to build. Provider-agnostic scoring layers, such as Twilio Lookup SMS Pumping Risk Score and Telesign Intelligence, work alongside any SMS provider, but require you to implement block and challenge logic on your side. If you're starting from scratch or evaluating providers, built-in protection is lower friction. If you have existing infrastructure you're not ready to migrate, a provider-agnostic scoring layer is the faster path to coverage.
Is Twilio's built-in SMS pumping protection enough?
It depends on which Twilio product you use and where your users are. Verify Fraud Guard blocks the destination prefix of suspected fraud, but it covers only SMS, not voice. SMS Pumping Protection for Programmable Messaging is included at no additional cost only in the US and Canada; other countries are priced separately. Lookup's SMS Pumping Risk Score returns a score, but your application has to enforce the decision, and Twilio doesn't recommend it for US or Canadian numbers. Teams that want every verification request scored and blocked before sending, without building their own enforcement logic, can use a verification API with fraud prevention built in, such as Prelude Verify. Either way, keep rate limits and destination controls in place.
What's Next?
SMS pumping is fundamentally an economic attack: attackers want your system to send messages that look legitimate but produce no legitimate users. The strongest defenses make the attack unprofitable by stopping suspicious traffic before the SMS is sent.
For teams evaluating a new verification stack, that means looking beyond delivery rates and API uptime. Ask how the provider detects AIT, what signals it uses, whether blocking happens before carrier dispatch, how false positives are handled, and whether you can fall back to another channel.
If SMS pumping is already affecting your verification costs, Prelude's Verify API has fraud prevention built in so that verification requests can be analyzed and suspicious traffic can be blocked before SMS dispatch. See how Verify works or get started for free.
For further reading:
Nearly 1 in 8 SMS verification requests was fraudulent in Prelude's 2025 dataset. Prelude analyzed more than 205 million authentication requests processed through its verification platform and identified 11.83% as fraudulent, representing 24.3 million blocked requests and an estimated $3.26 million in prevented SMS costs.
The attack can remain invisible until the invoice arrives or spend and traffic anomalies become obvious.
SMS pumping, also called artificially inflated traffic (AIT) or SMS toll fraud, works by automating requests to an OTP or verification endpoint. Those requests trigger SMS messages to premium-rate or otherwise high-cost numbers controlled by the attacker. The business pays for the messages; the attacker monetizes the resulting telecom traffic.
SMS pumping is also on the radar of telecom standards bodies. In February 2026, the International Telecommunication Union approved Recommendation E.371, which covers traffic that telecom operators treat as illegitimate, including traffic sent to premium-rate numbers (ITU-T E.371, 2026).
The attack has also become harder to detect with simple IP-based controls. Prelude's 2025 dataset found that residential proxy networks became the dominant attack infrastructure in its analyzed traffic, allowing attackers to distribute requests across large pools of apparently legitimate IP addresses.
The practical question in 2026 is therefore not whether you have rate limiting. It is whether you can make a reliable fraud decision before an SMS is sent.
This guide compares the main SMS pumping protection approaches available in 2026, from purpose-built verification APIs to provider-level filtering, phone-number intelligence, and application controls.
For how the attack works and the signals that expose it, see our guide on how to detect and prevent SMS pumping fraud.
What Separates Effective SMS Pumping Protection From Weak Protection?
The most important distinction is when the fraud decision happens.
Post-hoc detection identifies suspicious traffic after messages have already been sent. By then, the business has usually already incurred the messaging cost.
Pre-send protection evaluates the verification request before dispatch. If the request is blocked or routed to a non-SMS challenge before dispatch, the fraudulent SMS never reaches the carrier.
Six capabilities matter most:
Pre-send risk assessment. The system evaluates the request before SMS dispatch and can block or challenge high-risk traffic. If blocking happens after the SMS is sent, you've already paid for it.
Phone-number and telecom intelligence. Useful signals include number type, carrier, risky prefixes, premium-rate destinations, and historical reputation. These signals can be more useful than IP blocking alone, especially as residential proxies make IP-based controls less effective.
Velocity and behavioral detection. Sequential number ranges, bursts of requests, unusual country concentrations, poor verification conversion, and abnormal destination activity are common attack signals. Strong solutions surface these automatically.
Fallback handling. When a high-risk request is blocked, can your flow route to a different channel or prompt a step-up challenge? Blocking without fallback can create friction for legitimate users caught by overly aggressive filters.
Network-level intelligence. Providers that see traffic across many customers can identify coordinated attacks that would be difficult for an individual application to detect from its own traffic alone.
Actionable enforcement. A risk score is only useful if the system can turn it into an action before the SMS is sent: block, challenge, route to another channel, or apply additional verification.
Purpose-Built Verification Fraud Tools
These products combine OTP delivery with fraud controls. They are generally the lowest-effort option for teams building or rebuilding a phone-verification flow.
Prelude Verify API
Prelude's Verify API evaluates verification requests for fraud before sending the code. Suspicious requests can return a blocked status without sending an SMS. Prelude can also return a challenged state that routes suspicious requests through non-SMS and non-voice channels when that capability is enabled.
Its fraud detection combines telecom, behavioral, device, network, and historical signals. Prelude recommends sending additional signals including IP address, device ID, device platform, and device model to improve detection accuracy. These can be collected automatically via Prelude's frontend SDKs or passed from the backend.
Prelude's 2025 dataset found that 11.83% of analyzed authentication traffic was fraudulent, with Prelude successfully blocking 24.3 million fraudulent requests and preventing an estimated $3.26 million in SMS costs.
Verify also handles routing and fallback across multiple providers and channels, so fraud prevention can be part of the same verification infrastructure rather than a separate scoring API.
Best for: Teams building phone verification who want fraud prevention, routing, fallback, and verification analytics in one integration.
Limitation: Stronger fraud prevention benefits from additional signals such as IP address and device information. Teams need to collect and pass those signals, either directly or through Prelude's frontend SDKs, which is additional implementation work beyond a basic API integration.
Infobip Signals
Infobip Signals is designed specifically to detect artificially generated OTP traffic. It uses machine learning and adaptive learning algorithms to analyze signals including phone-number behavior, number ranges, phone-number types, message frequency, and error patterns.
Signals calculates a risk assessment for messages and can automatically block destinations or number ranges that exceed configured thresholds. Infobip says blocked traffic is not charged and does not count toward monthly volumes.
Best for: Teams already using Infobip for authentication who want automated AIT detection without building a separate fraud layer.
Limitation: Signals is part of the Infobip ecosystem. It is not a provider-agnostic scoring API that can be placed in front of another SMS provider.
Twilio Verify Fraud Guard
Twilio's Verify Fraud Guard blocks suspicious messages from being sent by a Verify Service. When it detects SMS pumping or unusual destination traffic, it blocks the destination prefix of the suspected fraud. It offers three protection levels: Basic, Standard, and Max, with Standard as the default. Twilio cites false-positive rates under 1% for Standard and under 2% for Max. Fraud Guard is part of Twilio Verify rather than a separate fraud API, and is turned on or off per Verify Service.
Fraud Guard protects only the SMS channel and uses behavioral and traffic signals to identify suspicious verification activity.
For teams using Twilio Programmable Messaging rather than Verify, Twilio offers a separate SMS Pumping Protection feature. Twilio provides it at no additional cost in the US and Canada. For other countries, pricing is listed on each country's SMS pricing page.
Best for: Teams already using Twilio Verify who want built-in SMS pumping protection without adding another provider.
Limitation: Verify Fraud Guard is part of Twilio Verify. Programmable Messaging customers use the separate SMS Pumping Protection feature.
Provider-Agnostic Risk Scoring
A different approach is to keep your existing SMS provider and insert a risk decision before the SMS send. This is useful when migrating providers would be expensive or disruptive.
Twilio Lookup SMS Pumping Risk Score
Twilio's Lookup API provides a dedicated SMS Pumping Risk Score that can be used regardless of which provider actually sends the SMS. The score uses Twilio's proprietary risk model and incorporates signals associated with SMS pumping activity.
Twilio returns a numeric SMS Pumping Risk Score from 0 to 100, with higher values indicating greater risk. Its documentation provides recommended ranges labeled Low, Mild, Moderate, and High. Your application can use the result to decide whether to send the message, add friction, or block the request. Twilio provides guidance for interpreting the score, but the enforcement policy remains under the customer's control.
The score is account-specific: it is based only on traffic Twilio sees on your account, not other customers' traffic. Twilio recommends querying the API before each user-generated OTP request rather than caching results, because the assessment can change as traffic patterns change. Twilio does not recommend using SMS Pumping Risk Score for US or Canadian phone numbers.
Best for: Teams that want a provider-agnostic SMS pumping signal without replacing their existing SMS infrastructure.
Limitation: Lookup provides the risk assessment; your application implements the enforcement logic. Each lookup also adds a separate API request and associated cost.
Telesign Intelligence
Telesign Intelligence provides a real-time risk recommendation that you can use to allow, flag, or block a number, along with reason codes. Its signals include phone type, carrier, IP and device data, and behavior patterns such as anomalous traffic and usage velocity. Telesign also positions its platform for detecting IRSF and other telecom fraud.
A useful characteristic is explainability. Rather than returning only a generic risk score, Telesign provides reason codes alongside the assessment, which can feed into an existing fraud engine.
Best for: Teams that need provider-agnostic phone intelligence and want detailed reason codes alongside a risk score.
Limitation: It is a scoring layer, not a complete verification flow. Your application implements the allow, challenge, or block decision, and each lookup adds an API call and some latency.
Messaging Infrastructure-Level Protection
Infrastructure-level controls are useful when your SMS provider already has visibility into the traffic being sent through its network.
AWS End User Messaging SMS Protect
AWS End User Messaging SMS Protect provides country-level controls and AIT risk filtering. Within a Protect configuration, each destination country can be configured as Allow, Block, Monitor, or Filter.
Monitor mode allows messages while reporting AIT risk. Filter mode uses AWS's AIT detection model to identify and block messages considered high risk.
Monitor and Filter modes incur additional charges for AIT risk evaluation. AWS also states that its statistical models do not guarantee complete protection and recommends additional application-level safeguards.
In Monitor mode, AWS adds its blocking recommendation to metrics and events, so teams can see what would be flagged before switching to Filter.
Best for: Teams already sending SMS through AWS that want a provider-level AIT filtering layer.
Limitation: SMS Protect is not a substitute for application-level fraud controls. Monitor and Filter modes add evaluation charges, and AWS recommends supplementing them with application safeguards.
Telnyx Verify API
Telnyx provides Verify for SMS and voice authentication, alongside Number Lookup for carrier and phone-number information.
Telnyx's fraud prevention guidance recommends rate limits per IP, phone number and user, restricting SMS to approved countries, and tracking the ratio of codes sent to codes verified. It flags sequential numbers, high-risk country codes, volume spikes and a verification conversion rate below 20% as possible signs of an attack.
Best for: Teams using Telnyx that want phone-number intelligence and flexible application-level controls around their verification flow.
Limitation: Number Lookup and the Verify API are not a complete fraud system by themselves. Effective SMS pumping prevention on Telnyx requires application-level fraud controls.
Google Cloud reCAPTCHA SMS Defense
Google's reCAPTCHA SMS Defense provides a risk score before an SMS is sent. Scores range from 0.0 to 1.0, with 0.0 indicating low confidence that SMS toll fraud is occurring and 1.0 indicating high confidence. Applications can use the assessment to allow or block an SMS before it is sent to the SMS provider.
The standalone reCAPTCHA SMS Defense capability is generally available (GA). Google announced its GA release on February 20, 2025.
For Firebase Authentication and Identity Platform, Google provides an integrated SMS Defense workflow that automatically assesses SMS authentication requests. The integration compares the risk score against a configured threshold and can prevent the SMS from being sent when the assessment exceeds that threshold.
This specific Firebase Authentication and Identity Platform integration is currently Preview (Pre-GA) and is subject to Google's Pre-GA Offerings Terms.
The integration supports two enforcement modes. In Audit mode, a failed toll-fraud assessment can trigger fallback verification methods rather than blocking the authentication flow. In Enforce mode, a failed assessment blocks the request and the SMS verification code is not sent. Google recommends starting in Audit mode to validate the configuration and monitor results before enabling enforcement.
Best for: Teams already using Firebase Authentication or Identity Platform that want native SMS toll-fraud protection with minimal additional application infrastructure.
Limitation: The Firebase Authentication and Identity Platform integration is currently Pre-GA. Teams using other authentication stacks can integrate SMS Defense directly through the reCAPTCHA API.
Baseline Application Controls
Dedicated fraud products are not a reason to skip basic application controls. These defenses are inexpensive, reduce attack volume, and give specialized detection systems fewer requests to evaluate.
Rate limits per phone number, IP, session and account. IP limits alone are no longer enough, because attackers spread requests across residential proxy networks.
Country and destination controls. Don't send verification SMS to countries you don't serve.
CAPTCHA on suspicious requests, as an extra layer rather than a primary defense.
Application context before a send, such as a session or account step, so an unauthenticated endpoint can't generate unlimited OTPs.
Conversion monitoring. A falling send-to-verify rate often shows an attack before send volume does.
For how to set these up, see how to stop SMS pumping on your signup form. For the warning signs to monitor, see how to detect SMS pumping fraud.
How the Approaches Compare
Approach | Pre-send enforcement | Phone / telecom intelligence | Provider-agnostic | Primary tradeoff |
Prelude Verify | Yes — block or challenge | Telecom, behavioral, device, network and historical signals. | No | Requires adopting Prelude for verification |
Infobip Signals | Yes | Number, range, type, behavioral signals | No | Requires Infobip |
Twilio Verify Fraud Guard | Yes | Destination traffic patterns | No | Requires Twilio Verify |
Twilio Lookup SMS Pumping Risk Score | Decision support; you enforce | SMS pumping-specific risk score | Yes | You build the enforcement logic |
AWS SMS Protect | Yes, at messaging layer | AIT risk model | No | Monitor/Filter modes add evaluation charges |
Telnyx Verify + Lookup | Partial / application-controlled | Carrier and line-type intelligence | No | Application-level fraud controls remain your responsibility |
Telesign Intelligence | Scoring; you enforce | Phone and fraud intelligence | Yes | Separate lookup and decision layer |
Google reCAPTCHA SMS Defense | Yes; Firebase/Identity Platform enforcement is Pre-GA | SMS toll-fraud risk signals | Via reCAPTCHA API | Standalone SMS Defense is GA; Firebase/Identity Platform integration is Pre-GA |
Baseline controls | Partial | Limited | Yes | Not sufficient alone against sophisticated attacks |
Choosing the Right Approach for Your Stack
If you're already on Prelude: Verify's fraud prevention is built in. Pass the recommended IP and device signals for stronger detection, and keep application-level rate limits and destination controls as additional layers.
If you're choosing a verification provider from scratch: Evaluate the fraud system as part of the verification product. Prelude Verify, Infobip Signals, and Twilio Verify all put fraud controls directly into the verification flow.
If you're on Twilio Verify: Fraud Guard is built in and offers Basic, Standard, and Max protection levels. Tune the level to your risk tolerance.
If you're on Twilio Programmable Messaging: Enable SMS Pumping Protection. If you need a provider-independent risk decision, consider Twilio's Lookup SMS Pumping Risk Score.
If you're on Infobip: Signals is the natural first layer. It is integrated with the Infobip messaging platform and can automatically block high-risk destinations and ranges.
If you're on AWS: Use SMS Protect for infrastructure-level AIT filtering, and keep application-level rate limiting, destination controls, and anomaly detection in place alongside it. AWS explicitly recommends additional application safeguards.
If you're on Telnyx: Use destination controls and Number Lookup, then implement the rate-limiting and anomaly-detection controls recommended in Telnyx's security guidance.
If you need a provider-agnostic layer: Twilio Lookup SMS Pumping Risk Score and Telesign Intelligence are both worth evaluating. Twilio's score is more narrowly focused on SMS pumping; Telesign provides broader phone and fraud intelligence with detailed reason codes.
If you're already on Firebase or Google Cloud: reCAPTCHA SMS Defense is GA as a standalone capability. The Firebase Authentication and Identity Platform integration is currently Preview (Pre-GA), so evaluate its launch stage accordingly for production use.
If you're early stage: Start with rate limiting, destination controls, spend alerts, and basic anomaly monitoring. Add pre-send fraud intelligence before SMS volume becomes large enough for a single attack to create a material financial loss.
FAQs
Do I need to switch SMS providers to get SMS pumping protection?
Not necessarily. Provider-agnostic options such as Twilio's Lookup SMS Pumping Risk Score and Telesign Intelligence can sit alongside an existing SMS provider, while application controls such as rate limiting and destination allowlists work independently of your provider. Switching providers can still make sense if you are starting from scratch or if your existing provider's fraud controls are insufficient. Purpose-built verification APIs can reduce the amount of fraud infrastructure you need to build and maintain yourself.
What is the difference between pre-send blocking and post-hoc detection?
Pre-send blocking evaluates each request before an SMS is dispatched. If a request is flagged as high-risk, no message is sent and no carrier cost is incurred. Post-hoc detection identifies fraudulent traffic after messages have already been sent, typically through billing anomaly alerts or dashboard reports. The practical difference is who absorbs the cost: pre-send blocking means fraudulent requests generate no charge; post-hoc detection means you've already paid for every fraudulent message before you knew it was fraudulent.
Will SMS pumping protection block legitimate users?
Yes, false positives are possible. The risk varies by product, configuration, traffic mix, and enforcement threshold. Most of the tools in this guide look at signals tied to SMS pumping, such as number ranges, number types, destinations and request velocity, rather than relying only on broad geographic blocks. The risk of false positives increases when teams use blunt controls like full country bans without phone number intelligence to distinguish real users from bots within those markets. Using layered signals rather than single-factor blocking can help reduce false positives.
Is CAPTCHA enough to stop SMS pumping?
No. CAPTCHA can make automated abuse more expensive and can filter low-effort bots, but it does not address the underlying telecom fraud signals that drive SMS pumping. Use CAPTCHA as one layer alongside rate limiting, destination controls, behavioral detection, and pre-send phone-number or network intelligence.
How do I choose between built-in verification fraud protection and a provider-agnostic scoring layer?
The main tradeoff is integration effort versus flexibility. Verification APIs with built-in fraud protection, such as Prelude Verify, Infobip Signals, and Twilio Verify Fraud Guard, apply it inside the API you're already calling, so there is no separate enforcement logic to build. Provider-agnostic scoring layers, such as Twilio Lookup SMS Pumping Risk Score and Telesign Intelligence, work alongside any SMS provider, but require you to implement block and challenge logic on your side. If you're starting from scratch or evaluating providers, built-in protection is lower friction. If you have existing infrastructure you're not ready to migrate, a provider-agnostic scoring layer is the faster path to coverage.
Is Twilio's built-in SMS pumping protection enough?
It depends on which Twilio product you use and where your users are. Verify Fraud Guard blocks the destination prefix of suspected fraud, but it covers only SMS, not voice. SMS Pumping Protection for Programmable Messaging is included at no additional cost only in the US and Canada; other countries are priced separately. Lookup's SMS Pumping Risk Score returns a score, but your application has to enforce the decision, and Twilio doesn't recommend it for US or Canadian numbers. Teams that want every verification request scored and blocked before sending, without building their own enforcement logic, can use a verification API with fraud prevention built in, such as Prelude Verify. Either way, keep rate limits and destination controls in place.
What's Next?
SMS pumping is fundamentally an economic attack: attackers want your system to send messages that look legitimate but produce no legitimate users. The strongest defenses make the attack unprofitable by stopping suspicious traffic before the SMS is sent.
For teams evaluating a new verification stack, that means looking beyond delivery rates and API uptime. Ask how the provider detects AIT, what signals it uses, whether blocking happens before carrier dispatch, how false positives are handled, and whether you can fall back to another channel.
If SMS pumping is already affecting your verification costs, Prelude's Verify API has fraud prevention built in so that verification requests can be analyzed and suspicious traffic can be blocked before SMS dispatch. See how Verify works or get started for free.
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