There are several places where the delivery of SMS and MMS messages might encounter issues, especially as they move between different infrastructure components.

Some common reasons for failure include:

  • Issues with the receiving device
  • Invalid number (landline, etc)
  • Cell carriers (spam filtering)
  • Telecom maintenance/outages
  • Using public link shorteners

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Receiving device

The receiving device may be a point of failure. If the device is turned off, out of service range, or otherwise unable to receive messages, the message may not be delivered. There can also be delivery problems if the device is roaming or moving quickly. These delivery failures should appear in the messaging logs with error codes 1009 or 1203.

Note: Failures with error code 1009 are the most common type of delivery issue.

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Invalid number

If the number you are messaging is invalid, the message will not be delivered. This can happen if the number is not formatted correctly, or if the number is not currently in service. These delivery failures should appear in the logs with error codes 1002 or 1350. If the number is a landline and cannot receive text messages, they will fail with error 1360. Please contact us if you believe you are seeing these errors incorrectly.

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Spam filtering

Telecom networks (cell carriers) are a common point of failure for SMS and MMS messages. They are also the most difficult to diagnose, as they are outside of our control.

The cell carriers have implemented various filtering systems aimed at preventing unwanted messaging like spam, fraud and abuse. These failures should appear in the logs with error code 1330 or 1065. Sometimes, filtered messages can also appear with error code 1009. If you believe your messages are being incorrectly filtered, please contact us and we can open an investigation with the affected carrier(s) to resolve the issue.

The cell carriers use machine learning to identify and block suspicious messages, so it is sometimes hard to determine exactly why a message was filtered. However, it is important to ensure that the messages you are sending are not spammy in nature.

Another potential cause of filtering is spam reports. Modern iOS and Android software includes a feature that lets recipients easily report a text message as spam if it’s coming from an unknown number. If messages you’re sending receive many of these spam reports, cell carriers may begin blocking some or all of your messages. To prevent this from happening, it’s important to ensure that recipients have clearly opted in to receive texts from you, and the texts you’re sending don’t look like unwanted spam to the recipient.

It is also possible for messages to be filtered if the message contents are significantly different from the use case or sample messages that were provided during the campaign registration process. For example, if you have registered a campaign under the “Account Alerts” use case, you should not send messages that are promotional in nature. This would be a violation of A2P 10DLC rules and could lead to message filtering. If you would like to update the sample messages attached to your campaign, please contact support.

Note: Sending links can sometimes trigger spam filters. See below for best practices.
It is important that you ensure all messages you send comply with our Messaging Policy.

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Network outages

U.S. cell carriers perform occasional maintenance on their systems, which can cause temporary delays or problems with message delivery. They will also sometimes experience SMS/MMS outages because of technical issues. These network problems can last anywhere from a few seconds to several hours. We will do our best to communicate these maintenance windows and outages to our customers as soon as we are made aware.

To comply with telecom industry rules and avoid message filtering, please ensure that links to websites embedded within a message do not conceal or obscure the sender’s identity. This means you should not send links that were shortened using Bitly, TinyURL or a similar public URL shortener. This will almost always result in the message being blocked. Instead, you should use a custom URL shortener on a domain that you control.

If you expect to be sending links in your messages, it is important that the sample messages you provide during the campaign registration process include examples of these links. This helps ensure that your messages are not incorrectly filtered as spam.