SMS delivery failures can occur for several reasons related to recipient phone numbers or carrier settings. This article explains common delivery issues and how to resolve them.
Test Before Sending
Always test your SMS campaigns with a small group before sending to your full list. This helps identify delivery issues early and ensures your recipients can receive messages.
Send a test message to 3-5 phone numbers that represent your recipient list (different carriers, regions, and phone types).
Common Delivery Issues
Landline Phone Numbers
Landlines cannot receive SMS messages. Your message will fail to deliver if the recipient number is a landline.
Solution: Remove landline numbers from your recipient list. Use only mobile phone numbers formatted in E.164 format.
Incompatible Phone Plans
Some phone plans cannot receive SMS messages. This includes certain pay-as-you-go plans and plans that require separate SMS packages.
Solution: Ask recipients to verify with their carrier that their plan includes SMS messaging. Recipients may need to add SMS capability to their plan.
Phone Out of Service
Phones without active service cannot receive SMS messages. ContactMonkey will retry delivery for one hour before timing out.
Solution: Verify the phone number is active and in service. Recipients should check their phone has network connectivity and isn't in airplane mode.
Recipient Carrier Blocks
Recipients may have blocks on their phone line that prevent SMS delivery. These blocks can be specific to certain numbers or to entire carriers.
Solution: Recipients should contact their carrier to check for blocks and request removal if needed. If they previously received unwanted messages, they may have set up carrier-level blocks.
Carrier-Level Restrictions
Some carriers block SMS messages from specific origins or services to prevent spam.
Solution: Contact ContactMonkey Support if you suspect carrier-level blocking. We use reputable SMS services and can investigate delivery issues with specific carriers.