How to Prevent SMS Messages from Being Blocked by Mobile Carriers

Why SMS Messages Get Blocked

While Kixie ensures that your SMS messages are sent, mobile carriers (e.g., AT&T, Verizon, T-Mobile) may block delivery due to various factors. Common reasons include:

• Your number is not registered for 10DLC

• Carrier-level filtering triggered by specific words or phrases associated with spam

• Anti-spam apps installed on the recipient’s phone

These blocks are outside of Kixie’s control, but by following best practices, you can significantly improve your message delivery rates.

You can verify if an SMS was delivered or undelivered within the SMS History section of the Kixie dashboard for your account or a given agent. These statuses are received when Kixie gets a DLR (Delivery Report) from the receiving carrier after we attempt to deliver the SMS message on your behalf.

Industry Requirement: 10DLC Registration

As of December 1st, 2024, registering for 10DLC (10-digit long code) is mandatory for sending SMS to U.S. numbers. Without registration, your messages will be blocked by carriers. This is the most important step to ensure successful SMS delivery. You should finish your 10DLC registration and wait for approval before attempting to send an SMS via an unregistered number because carriers still charge you for every attempt at sending an SMS, regardless of whether it was delivered or not.

Best Practices to Avoid SMS Blocking

1. Keep Messages Conversational and Personalized

• Keep texts short and natural, especially the first message to a new contact.
• Avoid overly promotional language or heavy marketing content in initial messages.
• Start with a simple introduction: "Hi (first name)." Wait a few seconds, then send the rest of your message.
• If sending a link, delay it until the third message in the sequence.

💡Tip: Automate this process using Zapier or CRM workflows to ensure consistency.

2. Avoid Using Shortened URLs

Due to high spam association, carriers automatically block shortened links (e.g., bit.ly, tinyurl.com, etc.). Instead:
✅ Use full, branded URLs (e.g., https://example.com/offer)
❌ Avoid repetitive URLs that appear suspicious (e.g., https://example.com/pages/pages/page1)

3. Limit Message Frequency & Volume

• Do not send identical messages repeatedly—carriers may flag them as spam.
• Personalize messages with [fname] tags or add variations.
• Keep daily SMS volume below 200 messages per number. If needed, use multiple registered numbers.
• Avoid sending multiple messages within 5–10 seconds of each other.

4. Optimize Message Length & Formatting

• SMS longer than 160 characters (GSM encoding without special characters) or 70 characters (Unicode encoding with special characters) may be split or blocked.

  • Use a message encoding tool to check whether your message is considered GSM or Unicode before sending. It also lets you see the total SMS units, which helps you calculate the cost. For more details, see our SMS Messaging Basics article.

• Avoid excessive punctuation, special characters, or ALL CAPS.

5. Call Before You Text

• Some mobile devices automatically filter SMS from unknown numbers or VoIP numbers—especially if there has been no prior call.
• Carriers may block messages from numbers with a poor incoming-to-outgoing ratio (e.g., sending 3x more texts than received).
• Place a quick call first to establish legitimacy.

6. Avoid Spam Triggers & Compliance Issues

• Refrain from using common spam trigger words (e.g., “FREE,” “LIMITED TIME,” “GUARANTEE,” “ACT NOW”).
• Respect opt-out requests—if a recipient replies STOP, you must not message them again. Kixie handles this block automatically, but you shouldn't attempt to bypass it, as it could lead to an AUP violation and fine.
• Follow carrier-specific rules such as adhering to SHAFT compliance. Do not attempt to send SMS if you fall into one of the following categories:
  ❌ High-risk financial services
  ❌ Real Estate sales or marketing
  ❌ Third-party lead generation
  ❌ Debt collection and forgiveness
  ❌ “Get rich quick” schemes or Multi-level marketing
  ❌ S.H.A.F.T. (Sex, Hate, Alcohol, Firearms, and Tobacco) sales
  ❌ Illegal substances (including cannabis)
  ❌ Gambling

⚠️ Violating these restrictions can result in:

• • Carrier infractions & fines ($500 to $2,000 per violation, depending upon severity)

  • Number suspension or removal

  • Complete account shutdown

What to Do If Your Messages Are Blocked

If you suspect your messages are being blocked:
✅ Check 10DLC Registration – Ensure your 10DLC Campaign is active and your number is properly registered with the 10DLC Campaign.
✅ Replace the SMS Number – Swap it out if a number was manually reported as spam to carriers.
✅ Reduce Message Volume – Space out messages and personalize them.
✅ Contact Kixie Support – If issues persist, reach out for further assistance.

For help setting up Auto-SMS or SMS Templates, or if you have any other questions regarding SMS or spam, email support@kixie.com, live chat with us using the "Chat With Support" option in the Kixie dashboard, or contact your Account Manager.