🚫 Smarter Message Sending: Blocking Known Failures Before They Happen

We’ve added a new pre-send validation layer to proactively block messages that are known to fail — such as sending to invalid numbers, landlines, opted-out contacts, or from misconfigured numbers.

Instead of submitting these messages to Twilio and waiting for them to fail, we now intercept them before they’re sent. This saves you time, money, and unnecessary confusion.

Messages that would trigger well-known error codes — such as sending to landlines (21635), opted-out contacts (21610), or invalid numbers (21211) — are now blocked automatically.

Contacts that repeatedly trigger delivery errors (such as STOP replies or landlines) are marked with appropriate DND (Do Not Disturb) flags to prevent future sends, while still allowing retries in temporary situations (like a phone being switched off).

If a message is blocked before sending, you’ll receive an explanation of why it was blocked, so you’re not left guessing.

✉️ Fewer failed messages: We prevent what’s preventable, so your delivery rate improves.

💸 Lower messaging costs: By avoiding Twilio API calls on known failures, you save credits.

💡 More clarity for you: You receive meaningful feedback upfront, not error codes afterwards.

🙌 Better customer experience: There’s no need to wait for errors, submit support tickets, or guess what went wrong.

Examples of messages that are now blocked before they are sent:

Sending to opted-out contacts (21610)

Trying to reach a landline (21635, 30006)

Using a sender number that isn’t SMS-capable (21661)

Messaging before A2P campaign registration completes (30034)

More than a dozen other such predictable failure types.

We’ve also introduced intelligent DND behaviour: some contacts are permanently excluded, while others are only temporarily excluded, depending on the reason for failure.

We only block messages where the failure is highly predictable or guaranteed. In edge cases (e.g. carrier issues), messages will still flow through Twilio and receive the usual post-send handling.

This update is applicable across all messaging surfaces: Conversations, Campaigns, and Bulk Messaging.

This change is part of our ongoing effort to help you send smarter, not harder. By eliminating avoidable failures and providing visibility upfront, we’re making messaging more efficient and reliable — without requiring any extra effort from you.

As always, we’re here if you have questions or suggestions on how to improve further.