Why it matters
A Delivered status confirms that the carrier accepted the message, but it does not guarantee that the message reached the recipient’s device. Recognizing the reasons for these discrepancies helps you diagnose delivery issues and take the appropriate corrective steps.
Key Concepts
Delivered status: Confirmation from the carrier that the message was handed off to the destination network.
Carrier filtering: When a carrier accepts a message but later blocks it before it reaches the device.
Long code (10DLC): Standard 10-digit numbers used for A2P messaging in the US and Canada.
Short code / Toll-free SMS: Alternative sending options with higher deliverability under certain regulatory conditions.
Understanding Delivery Statuses
When Whippy sends an SMS:
The message is first marked Sent.
The status updates to Delivered once the carrier confirms it has been passed to the destination network.
However, some carriers do not provide accurate handset-level delivery receipts, resulting in false Delivered statuses.
Why Messages May Show Delivered but Are Not Received
Device-specific issues:
If only one contact reports the problem, the issue is likely with their mobile device (e.g., storage, phone settings, SIM card, or signal).
Carrier or network issues:
If multiple recipients are affected, causes may include:
Carrier filtering
Local telecom network problems
Infrastructure limitations in the destination country
Temporary outages
A2P blocking on long code numbers (US & Canada):
Messages sent using standard 10-digit long codes may be flagged or blocked due to regulatory filtering. Messages can still show as Delivered because the carrier accepted the message before filtering it.
International routing issues:
Some countries have strict messaging rules, infrastructure challenges, or require pre-registration of sender IDs.
Step-by-Step: Troubleshoot Delivered but Undelivered SMS
Check how many recipients are affected.
One recipient → device issue likely.
Several recipients → carrier or network-related.
If messaging US/Canada via long code, assess filtering risk.
Carriers may silently block A2P long-code messages.
Whippy normally receives an error when filtering occurs, but not always.
Consider switching to an alternative sending method.
Short codes: High deliverability; ideal for high-volume or compliance-sensitive traffic.
Toll-free numbers: Effective for many business needs, but not suitable for promotional marketing.
Note: In Canada, toll-free traffic faces the same filtering rules as long code.
Verify message compliance.
Review local regulations and ensure no restricted content is included.
Investigate international constraints.
When sending abroad, confirm whether:
Sender ID registration is required
Carriers apply stricter filtering
Local infrastructure is inconsistent
Tips and Best Practices
Check multiple conversations to identify if the issue is widespread.
Use properly registered numbers for A2P traffic in the US and Canada.
Follow all local SMS regulations for the destination country.
Ensure message content meets standard SMS compliance guidelines.
Consider switching to short code or toll-free for improved reliability where appropriate.
Troubleshooting
Issue | Possible Cause | Fix |
Messages show Delivered but not received | Device-level issue | Ask contact to restart device, clear storage, or check signal |
Multiple contacts not receiving messages | Carrier filtering or network issue | Review message content, check regulations, consider short code/toll-free |
Long code messages inconsistent | A2P filtering in US/Canada | Switch to verified 10DLC, short code, or toll-free |
International messages undelivered | Local restrictions or sender ID rules | Confirm if sender ID registration is required |
No error returned | Carrier reports Delivered even when filtered | Monitor patterns and adjust sending number or route |