SMS delivery failure is one of the most costly problems in business messaging. You write the message, pay for delivery, and assume it reaches the recipient — but a significant percentage of messages silently fail. Understanding the common causes of SMS delivery failure and knowing how to fix SMS delivery issues before they happen can save thousands in wasted spend and dramatically improve campaign performance.
1. Invalid or Mistyped Phone Numbers
Some numbers simply do not exist. Typos, extra digits, or missing country codes cause SMS messages to fail immediately at the carrier level.
Fix it: Use a phone validation API to verify number syntax, length, and format before sending. Standardize formats (like E.164) for global consistency.
2. Landline or VoIP Numbers
Not all numbers can receive text messages. Landlines do not support SMS, and many VoIP providers block or drop inbound SMS by default.
Fix it: Run line type detection on all numbers before sending. Only deliver SMS to mobile lines with proven deliverability.
3. Suspended or Disconnected Lines
Sometimes a number was once valid but has been suspended, deactivated, or placed in “past-due” status by the carrier. Messages to these numbers will silently fail.
Fix it: Use real-time carrier lookup and deactivation checks to detect temporarily out-of-service numbers before messaging.
4. Incorrect Carrier Routing
If your SMS platform routes the message to the wrong carrier — often due to outdated portability data — the message may fail or disappear entirely.
Fix it: Use a validation tool that supports LRN (Local Routing Number) lookup and real-time carrier detection. This ensures the message goes to the number’s current carrier, not its original one. CheckThatPhone includes LRN data in its standard API response.
5. Blocked by Aggregator or Carrier
Some carriers block messages from certain senders or routes, especially if the sender has poor reputation or violates opt-in rules. You might not even receive a delivery report in these cases.
Fix it: Use clean opt-in data, avoid spammy language, and ensure your sender ID is registered where required. Also, monitor your SMS performance across different routes and providers.
6. Wrong Time or Region
Messages sent during quiet hours or to the wrong region may be delayed or filtered. Some carriers enforce quiet periods for consumer protection.
Fix it: Use GeoIP and timezone data to send messages at the right local time. This improves both deliverability and engagement.
Bonus: Use “Action” Recommendations
Advanced validation platforms like CheckThatPhone do not just return data — they suggest what to do. Based on carrier, line status, and history, you get an action field like:
- send — safe to message
- wait — recently suspended
- skip — number unreachable or invalid
This lets you automate better decision-making without writing custom logic for every edge case.
Getting Started
You cannot afford to guess when it comes to SMS delivery. Addressing the root causes of SMS delivery failure before messages are sent is the single most effective way to fix SMS delivery performance at scale. With the right validation tools in place, you will increase delivery success, reduce spend on failed messages, avoid frustration for users, and boost ROI across all SMS campaigns.
Read the CheckThatPhone documentation to see how real-time validation and action recommendations work, or explore our pricing plans to start filtering invalid numbers before your next send.