Your messages leave Twilio with no errors but some users — especially on one carrier — never get them. This is carrier-level filtering, and the fix depends on which carrier and why.
Each US carrier maintains its own registration database. Twilio submits your A2P campaign to carriers through TCR (The Campaign Registry), but processing is carrier-specific. AT&T, Verizon, and T-Mobile each have separate approval timelines. Check your campaign status per-carrier in Twilio Console under Messaging > Compliance.
Carrier spam filters use keyword lists, link patterns, and sender reputation. URLs without HTTPS, shortened links (bit.ly, tinyurl), and phrases like 'free', 'win', 'urgent', or 'click now' are common triggers. Send a plain text message with no links to test if content is the issue.
If your number previously sent high volumes of spam or had complaint rates above carrier thresholds, it may be on a per-carrier blocklist. Check Twilio's number reputation via Console or use a number lookup service. If blocked, you may need to provision a new number and migrate traffic.
Sudden spikes above your registered throughput — especially burst sends — can cause carriers to temporarily block the number. Use Twilio messaging services with multiple numbers to distribute load, and ramp volume gradually rather than blasting.
Short codes and long codes have different carrier relationships. If your campaign recently migrated number types, the new number may not yet be approved at the carrier level for your message use case.
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