Name: twilio-sms-send-message
Author: twilio

SMS and MMS deep-dive reference. Covers SMS-specific error codes, message filtering troubleshooting ("Messages Being Filtered or Blocked?" diagnostic checklist), MMS media support (US/CA/AU only), and SMS pumping indicators. For sending SMS, use twilio-send-message instead. Use this skill only when

Overview SMS is one channel in Twilio's Messaging platform. All channels — SMS, WhatsApp, RCS, Facebook Messenger — share the same messages.create() API. See twilio messaging overview for the full channel comparison and onboarding sequence. When to use SMS When to consider alternatives Reach any phone number globally Need rich media outside US/CA/AU → WhatsApp No app install required Opted in audience prefers chat apps → WhatsApp Time sensitive alerts (OTP, outage) Marketing campaigns → twilio marketing promotions advisor Regulatory/compliance requires SMS Cost sensitive high volume → WhatsApp (lower per msg cost in many markets) For production SMS: Use a Messaging Service ( messagingServiceSid ) instead of a raw from number. It enables sender pool management, compliance toolkit, SMS pumping protection, link shortening, and message scheduling. See twilio messaging services . Every outbound SMS requires a from Twilio number (or messagingServiceSid ) and a to recipient — both in E.164 format. Prerequisites Twilio account with an SMS capable phone number — New to Twilio? See twilio account setup for signup, getting a number, and trial limitations Environment variables: TWILIO ACCOUNT SID TWILIO AUTH TOKEN — See twilio iam auth setup for credential setup and best practices SDK: pip install twilio / npm install twilio Quickstart Python Node.js Key Patterns Send MMS (with media) Python Node.js Supported media types: images (JPEG, PNG, GIF), PDF, audio, video. Max 5 MB per message. Send via Messaging Service (recommended for scale) Use messagingServiceSid instead of from — Twilio picks the best sender automatically from your pool. Python Node.js Track Delivery Status Python Node.js Twilio POSTs to your URL at each transition: queued → sent → delivered (or failed / undelivered ). Response Fields Field Description sid Message identifier ( SM... ) status queued , sent , delivered , undelivered , failed error code Populated on failure error message Human readable description price Cost (populated after delivery) date sent UTC timestamp Common Errors Code Meaning Fix 21211 Invalid to number Validate E.164 format 21408 Permission to send to region not enabled Enable geo permissions in Console 21610 Number is on blocklist (opted out) Do not retry; respect opt out 30003 Unreachable destination Carrier cannot deliver; try later 30007 Message filtered as spam Review content and sender reputation 30034 Message from unregistered number Complete A2P 10DLC registration — see twilio compliance onboarding 30450 SMS pumping detected Message blocked by SMS pumping protection — see twilio messaging services Messages Being Filtered or Blocked? If your messages aren't being delivered, check these causes in order: 1. Unregistered sender (error 30034) — US 10DLC numbers must be registered. See twilio compliance onboarding 2. Spam filtered (error 30007) — Carrier flagged content. Check: opt out language included? URL shorteners avoided? Content matches registered campaign? 3. Opted out recipient (error 21610) — Recipient sent STOP. Do not retry. See twilio compliance traffic 4. Geo permissions disabled (error 21408) — Enable the destination country in Console Messaging Settings Geo Permissions. See twilio security hardening 5. SMS pumping (error 30450) — Artificial traffic detected. Whitelist known prefixes via Global Safe List. See twilio messaging services 6. Account suspended — Check Console for account status notifications. See twilio account setup For delivery event tracking, set up StatusCallbacks or use twilio debugging observability . CANNOT Cannot send without E.164 format — Both from and to must be + followed by country code and number Cannot send to unverified numbers on trial accounts — Upgrade to paid or verify recipient numbers first Cannot send MMS outside US, Canada, and Australia — MMS is only supported on US/CA/AU numbers; for international rich media use WhatsApp Cannot exceed 1,600 characters per message — Longer messages are automatically split into segments (each billed separately) Cannot prevent SMS pumping without a Messaging Service — Enable SMS pumping protection via Messaging Services to prevent artificial traffic inflation. See twilio messaging services Next Steps Channel overview and onboarding guide: twilio messaging overview Receive inbound SMS and delivery status: twilio messaging webhooks Manage sender pools at scale: twilio messaging services US compliance for A2P traffic: twilio compliance onboarding Send via WhatsApp instead: twilio whatsapp send message