SMS firewall
What is SMS firewall?
An SMS firewall is a carrier-operated (or carrier-facing) system that inspects inbound and outbound SMS traffic in real time to detect and block fraud, spam, and unauthorized routing — most notably artificial inflation of traffic (AIT) and grey-route messages that bypass a carrier's commercial agreements. Carriers deploy SMS firewalls to protect revenue and subscriber experience, and legitimate A2P senders can get caught in overly aggressive filtering if their traffic pattern or route resembles the abuse the firewall is tuned to catch.
More detail
Artificial inflation of traffic (AIT) fraud typically involves generating fake OTP or verification traffic to premium-rate numbers to earn a cut of the resulting carrier fees — a major driver behind stricter firewall filtering globally.
Sending through a properly licensed, registered route (a verified 10DLC campaign or a carrier-approved aggregator) is the main way a legitimate sender avoids getting flagged by carrier SMS firewalls.
Frequently asked
- Why did my legitimate SMS campaign suddenly get filtered?
- Carrier SMS firewalls block traffic patterns that resemble fraud or grey routing, and a legitimate campaign can occasionally get caught in that filtering if its volume, route, or content pattern looks similar to abuse the firewall targets.
- What is a grey route in the context of SMS firewalls?
- A grey route is a message path that bypasses a carrier's official commercial messaging agreements — typically routed to look like person-to-person traffic — which SMS firewalls are specifically built to detect and block.
See also
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