Wireless carriers, including AT&T, Verizon, T-Mobile, and Sprint, monitor SMS sent over their networks to prevent the delivery of spam. When messages are sent from a 10-digit long number, carriers will sometimes filter out texts that their systems have flagged. One way to improve deliverability is by using several sending numbers to avoid having all the volume and traffic come through one number. This article will share how many long numbers you should have and how to add them.
As of October 1, 2021, Klaviyo no longer supports the use of long numbers.
Recommended Number of Long Codes
In general, it is better to use a toll-free number than a long number. Toll-free numbers are better for deliverability and, in many cases, can be verified.
However, if you do want to use a long number instead, it's important to limit how many subscribers you send a message to from any one long number. Wireless carriers have stricter SMS filtering policies for long numbers when they are used for application-to-person texting. A message sent from a single long number to too many people will likely not be delivered. However, SMS messages are priced based on how many you send, not those that are delivered.
Thus, the number of long numbers an account should have is based on how many SMS subscribers you have. A best practice is to have one long code per every 200 SMS subscribers that you send to regularly.
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Check out these articles to learn more about SMS deliverability: