Troubleshooting Deliverability

Understand what makes your messages more likely to be delivered.

The content of your message doesn't match the number you're using

Carriers use filtering systems to detect spam and misuse of numbers. These filtering systems work much like email filtering, where certain content may result in the carrier blocking your message. Content filtering systems will look at both the text of the message itself and the number sending the message.

Automated content such as marketing messages, appointment reminders, chatbots/virtual assistants, notifications, and one-time passwords (OTPs)/PIN codes, is typically identified by carriers as application-to-person (A2P) messaging. In the US and Canada, A2P is restricted by most major carriers to short code (numbers with only 5-6 digits) and toll-free numbers. Verizon has recently allowed A2P messaging on local long code numbers, referred to as 10DLC, although this only applies to Verizon subscribers. Sending automated content over a local long code number will most likely result in your messages being blocked by carriers.

If you're trying to send automated content and are having deliverability issues, make sure your number is approved for A2P.

Long Code

Toll-Free

Short Code

Messaging Use Case

Person-to-Person (P2P):

• SMS customer service
• anonymous communication
• SMS communication with a rideshare or delivery service

Application-to-Person (A2P):

• SMS marketing
• appointment reminders
• chat bots
• notifications
• one-time passwords (OTPs)

High Volume A2P:

• alerts
• marketing
• reminders


The volume of messages is too great for the number you're using

Carrier filtering systems also monitor the rate at which messages are being sent. Local long code numbers are designed to handle person-to-person messaging, and allow 1 message per second. Exceeding that rate will increase the risk of your messages being blocked. Toll-free numbers are designed to handle business-related messaging and have a slightly greater volume of 3 messages per second allowed. Short code numbers are specifically designed for sending a large volume of messages, allowing thousands of messages to be sent per second.

If you're having delivery issues with sending a large number of messages, consider switching to a higher volume number. If you're specifically interested in moving to a short code, contact support to discuss your use case.

Long Code

Toll-Free

Short Code

Messages per Second

1 msg/sec

3 msg/sec

This number can be increased for upgraded accounts. Contact support for more information.

100 msg/sec

Contact support if you are interested in using short codes.


Your message is too long

Long messages are broken into segments that are sent and then stitched back together for the recipient. This process is called concatenation and most carriers in the US and Canada support it. Although it's not very common, sometimes individual segments can get dropped by the carrier. When messages have more than 10 segments, the chance of a carrier failure goes up. For more details on concatenation, please reference our concatenation guide.

If you try to send a long message and have issues with delivery, try shortening the message. To check how many segments your message will be broken up into, you can use this handy tool.


Your message may have been filtered as spam

Carriers use filtering systems to detect spam and misuse of numbers. These filtering systems work much like email filtering, where certain content may result in the carrier blocking your message. Content filtering systems will look at both the text of the message itself and the number sending the message.

Please review CTIA Best Practices to protect your messages from inadvertently being flagged as spam or nuisance messages.