Your contacts complained to their carrier that they were receiving unwanted messages.

Carriers are filtering you based on content (objectionable keywords or links)

Carriers are filtering you because the volume of messages you are sending from is too large.

You are sending similar or identical content from a long code to many multiple numbers within a short period time.

Your messages have been caught by the carrier filter for some unknown reason. Carriers do not advertise how their spam filters work to avoid reverse engineering.

Be sure you have a good user experience and clear opt-out instructions.

Avoid sending questionable content. See which types of messages count as questionable content.

Send fewer messages from each long code.

See the content and volume guidelines for each country you are sending SMS to. (On the coverage page, search for the countries you want to send and receive messages in.) For example, in the US you should adjust your message send rate so it is more consistent with typical human operation per CTIA's guideline in Messaging Principles and Best Practices. The CTIA advises that each long code phone number should stay under 15-60 messages per minute and under 200 unique recipients a day.

Consider using Copilot and add more numbers to your Messaging Service. This will distribute the load across multiple numbers.

Consider using a Short Code to send high-volume traffic in the US, Canada, and the UK. Short codes are pre-approved by carriers to send at high volume. They cost more and take a long time to get, but they are don't get filtered like standard long code numbers. Contact Medallia Concierge Sales if you'd like help deciding if short codes would be a good fit for you.

Wait a period of time before sending messages again. When most carriers blacklist numbers they have a cooling off period before they can send again.