How to Avoid Outbound SMS Rejection


What are some best practices to avoid having my outbound SMS rejected?

Applies To

  • Outbound SMS
  • Spam
  • Encoding
  • Number Format


Use the Right Encoding

Not all phones support all languages. For example, sending a Chinese message to a French phone will get to the handset but will not display to the user. Sending binary messages to an iPhone won’t work, either.

Don't Spam

Not only is spamming illegal, more often than not, it doesn’t work. Most likely the message will not arrive at the handset and you will still be stuck paying for it. Spam filters have become very good at detecting spam attacks.

Certain carriers filter keywords (such as the carrier’s own name) to prevent brand theft and scams.

Vary the Wording in Your Message Body

When sending campaigns, it is better to randomize the order of the body of the message, if you can. If you are sending an opted-in marketing campaign or many password codes at once, come up with more than one version of the content and change it randomly. For example:

  • Message 1: Your Pin Code is 2234
  • Message 2: Please enter 2234 into your application to verify your account

Format the Destination Address

Make sure to format the To field in international format, including the correct country code. Refer to the ITU’s International Numbering Resources.

It is not necessary to include dialing prefixes such as + or 00, but if you have no choice (because of compatibility with other services for example) Vonage can accommodate this formatting.

If sending for your clients, do not rely on them to use the correct formatting. There are libraries available that can help you automatically find the right format, such as Google Lib.

A badly formatted number will be rejected, so it is recommended that you track rejections and optimize according to this feedback.

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