Carrier Filtering: What It Is and How to Keep Your SMS Messages Delivered

Carrier Filtering: Why Your Texts Get Blocked and How to Fix It

Carrier filtering is when a mobile network (AT&T, T-Mobile, Verizon and others) decides a business text looks like spam and blocks it before it reaches the phone. Your platform may mark the message as sent, and the customer never sees it. If your delivery rate suddenly drops, this is the first thing to check.

Is it really silent?

Not always. On many platforms a filtered message comes back as a failure with an error code. Twilio-based platforms, for example, report it as error 30007, “carrier violation.” Other providers use their own codes. The catch is that the error often says only that something was filtered, not why, so you have to work backwards. Filtering can also differ from one carrier to the next: a message blocked by one can be delivered by another, depending on its content, volume and the sender’s history.

What triggers it

• Unregistered numbers. In the US, business texts from regular 10-digit numbers must be registered through 10DLC. Unregistered traffic is now heavily limited or blocked, and the exact timeline depends on the carrier and your provider.
• Public link shorteners. Links from Bitly, TinyURL and similar services are a very common trigger. If you must shorten, use a branded domain that redirects to your own site.
• A message that doesn’t match what you registered. Carriers compare your texts with the use case and samples you submitted.
• Missing opt-in proof or opt-out wording.
• Spam patterns. Heavy capitalisation, pressure language, repeated near-identical blasts.
• Complaints and high opt-out rates, which damage your sender reputation over time.
• Sudden volume spikes from a number that normally sends little. Carriers also cap daily volume based on your trust level.
• Restricted content, such as certain loan, gambling or cannabis messages, which carriers limit regardless of consent.

If your messages are being filtered, check in this order

1. Registration. Is your brand and campaign approved, and is the number attached to it?
2. The link. Remove any public shortener and test with a full URL on your own domain.
3. The text. Does it match your registered samples? Does it name your business and include opt-out wording?
4. Consent. Can you show how each recipient opted in, including the disclosure wording on your form?
5. Your list. Remove old, recycled or landline numbers.
6. The pattern. Did you send much more than usual, or change numbers lately?
7. Ask your provider. Send them several examples with timestamps and error codes so they can escalate to the carrier if you think the block is a mistake.

How to avoid it

• Register before you send, and keep the registration up to date.
• Send only to people who opted in, and honor STOP replies.
• Use one consistent sender and a branded link domain.
• Write like a person: plain wording, your company name, one clear purpose.
• Increase volume gradually.
• Watch your delivery reports every week, not only after a bad send.

If you send in India

India’s system works on registration, too. Senders and message templates must be registered on the telecom operators’ DLT platforms, and a message that doesn’t match its registered template can be rejected. Check your provider’s guidance for the current rules.

Carrier filtering and Salesforce

Filtering depends on your numbers, registration and message content, not on the CRM. What Salesforce can help with is visibility: when delivery status and failures are logged on the record, you can spot a drop quickly and see which contacts were affected.

MessageBlink is a Salesforce-native SMS and WhatsApp app that logs message status on the record and handles STOP replies. Registration and sender reputation are set up with your SMS provider, so confirm that process before launching a campaign.