Carrier Filtering
Filtering is the carriers' spam wall. Registration, clean URLs, matched use case, and low complaint rates are what keep you off it.
US carriers run machine-learning filters over A2P traffic, scoring registration status, content patterns, URL reputation, recipient complaint rates, and volume spikes.
Filtering is intentionally opaque: messages can show as delivered to the provider but never reach handsets, or return generic codes (Twilio 30007/30032 class errors). Common triggers include unregistered traffic, link shorteners like bit.ly, declared-vs-actual use-case mismatch, segment spikes from a cold number, and SHAFT content (sex, hate, alcohol, firearms, tobacco) outside permitted programs.
Recovery is procedural: fix registration, replace shared shorteners with branded domains, warm up volume gradually, and bring opt-in quality up so complaint rates fall below carrier thresholds.
Frequently asked questions
Related glossary terms
10DLC (10-Digit Long Code) is the US carrier-mandated framework for sending Application-to-Person SMS from local 10-digit numbers, requiring brand and campaign registration with The Campaign Registry.
Carrier surcharges are per-segment fees ($0.0025-$0.01 typical) that US carriers charge on A2P SMS, passed through by providers on top of the base message price. Registered traffic pays lower rates than unregistered.
Opt-out rate is the percentage of recipients who unsubscribe (reply STOP) per campaign or period. Healthy SMS programs run well under 1% per campaign; sustained spikes signal consent-quality or relevance problems carriers also notice.