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Understanding What It Means When a Text Message to a Lead Is 'Undelivered'

Learn why some texts are marked “Undelivered,” what causes it, and how to reduce filtered messages.

 

Why This Feature Matters

 

 

Text deliverability issues can impact your ability to connect with leads—especially if carriers mark messages as spam. This article clarifies:

 

  • Why undelivered messages occur

  • What the Twilio error codes mean

  • How mobile carriers filter SMS content

  • What Sierra and clients can do to mitigate issues

 

 

 

Step-by-Step Instructions

 

 

 

When a Message Is Marked “Undelivered”

 

 

  1. A message is marked “Undelivered” in the lead detail page.

  2. Sierra returns a Twilio error code (e.g., 30003, 30004, etc.).

  3. The corresponding system note includes:

     

    • The error code

    • A link to this KB article for further context

     

 

 

 

What the Error Codes Mean

 

 

  • 30003 – Unreachable destination handset

  • 30004 – Message blocked

  • 30005 – Unknown destination handset

  • 30006 – Landline or unreachable carrier

  • 30007 – Carrier violation

  • 30008 – Unknown error

 

 

💡 In May 2020, 82.8% of undelivered messages returned code 30003, indicating carrier filtering is the most common reason.

 

 

Sierra’s Monitoring & Findings

 

 

  • Some leads receive both delivered and undelivered texts within the same thread.

  • Filtering appears to be per-message, not account-wide—but if a number is flagged, future messages are more likely to be filtered.

  • Most filtering is triggered by high volume and repetitive message content.

 

 

 

Twilio’s Response

 

 

  • Carriers may classify repetitive content as automated application-to-person (A2P) traffic.

  • Once filtered, a number’s reputation is negatively impacted, even for unique messages.

 

 

 

Best Practices

 

 

  • Avoid repetitive or templated content in bulk SMS.

  • Space out text sends—especially from new numbers.

  • Use smart filters to prioritize active leads and avoid unnecessary bulk sends.

  • Avoid aggressive high-volume texting during short time windows.

  • Rotate or replace Dialer numbers if they begin showing high undelivered rates.

 

 

 

Troubleshooting Common Issues

 

 

Issue: High percentage of undelivered messages

Fix: Try retiring and forwarding from the affected Dialer number. Use a new number and reduce outbound SMS volume.

 

Issue: Lead never receives texts despite appearing valid

Fix: Check the Line Type using Twilio Lookup in the lead detail. If it’s a landline or VOIP, SMS may not be supported.

 

 

FAQs

 

 

Q: Is Sierra’s system causing messages to fail?

A: No. Messages leave Sierra and Twilio successfully—delivery failures occur at the carrier level, based on filtering.

 

Q: Are we charged for filtered messages?

A: Yes. Twilio bills Sierra for every message sent, regardless of carrier filtering.

 

Q: Will all undelivered messages have an error code?

A: Yes. Sierra displays Twilio’s error codes in the system note.

 

Q: Can I mark a lead as opted out after an undelivered message?

A: No. Since many leads receive some messages successfully, auto-opting out would risk blocking real communication.