I’m constantly asked questions in my trainings about broadcast and peer-to-peer mobile messaging deliverability. So with the help of Twilio, I’ve done my best to answer some of these frequently asked questions about SMS/MMS filtering done by wireless carriers that can affect the delivery of your text messages. Filtering by Wireless Carriers is often done to comply with federal (TCPA), state, or local regulations, or wireless carriers’ messaging policies established by the CTIA. Unlike email filters, carrier filters don’t send these messages to a place where you can simply find them later, your messages are completely blocked or flagged to block if it happens again on the same number.

Filtering can vary widely between carriers and countries – this post’s guidance is limited to the U.S. and Canada. So let’s break it down.

Why do Wireless Carriers have Filtering Systems?

Wireless carriers have filtering systems for two reasons:

1. A2P Filters: Enforcing rules or regulations about what types of messaging are allowed to that country or mobile network

In the U.S. and Canada, application-to-person (A2P) type messaging is typically broadcast or bulk texting, and not allowed to be sent using local 10-digit long code phone numbers. A2P traffic is supposed to be sent using shortcodes, 5-6 digit numbers which are approved in advance by all the mobile carriers in the country for A2P and broadcast texting. Toll-Free numbers are also approved for some types of broadcast A2P messaging. If a platform allows you to send to more than one person at a time from a 10-digit long code, your messages will likely be blocked by the carriers. Deliverability stats are not offered on 10-digit long codes for bulk messaging and therefore you’ll never know if your messages went through or not.

As of August 2019, the only exception is Verizon Wireless with its upcoming “10DLC” A2P long code product. But 10DLC (ie. 10 Digit Long codes) have not been offered by the other carriers and are therefore not useful.

2. SPAM Filters: Protecting mobile subscribers from unwanted messaging such as spam, fraud, or abuse

“When a mobile subscriber receives messages they find objectionable, they may file complaints, seek damages, or simply stop being a customer. All of these things reduce revenue or increase costs for carriers. Thus, it is in the best interest of carriers to protect mobile subscribers from what they consider to be objectionable content.” – Twilio

How do Wireless Carriers Filter Messages?

“There is no standard practice for carrier filtering across all carriers. Filtering can range from a simple static list of prohibited terms to advanced machine learning systems that constantly adapt based on the messages passing through them. Regardless of the system, carriers keep their filtering systems closely guarded secrets. Due to the ambiguous nature of these filtering mechanisms, Twilio is unable to say definitively how these systems work, or why a particular message was filtered.” – Twilio

Only messages sent from 10-digit long codes and Toll-Free numbers are subject to this type of filtering. The primary method of texting that uses 10-digit local numbers is peer-to-peer (P2P) text messaging. Sometimes including a bit.ly or other short URL in a message can trigger these filters, or messages that include words in all CAPS can hurt deliverabilty. Again it truly varies by carrier and these filter algorithms are constantly changing. P2P Texting Vendors like Hustle and GetThru are constantly providing guidance on new best practices around message content for deliverability for this reason.

How do I Know if my Messages are Being Filtered?

No one can predict filtering, and we don’t always know for certain when a message has been filtered by a carrier. According to Twilio, some carriers may even falsely report filtered messages as delivered to prevent spammers from reverse engineering filtering systems. In other cases, we can know that a particular message has been filtered based on the error code, which is usually: Error 30007: Message Delivery – Carrier Violation, and that message will be marked as undelivered.

How do I improve my Message Deliverability?

If you are starting a messaging campaign or program in the U.S. and Canada, or you suspect your messages are being filtered, we recommend you first check Twilio’s SMS Carrier Filtering in the United States and Canada.

You should also follow these best practices to reduce the risk of your messages being blocked:

Provide a good user experience: Users are likely to report confusing or unwanted messages to their carrier. When these messages are reported to carriers, it becomes very likely that future messages from the same number (or those with similar content) will be filtered.

Always identify yourself as the sender: In some cases, the user may have forgotten that they opted-in to receive messages, so be sure to always identify your organization in the message.

How the message is formatted and written is important. Overly long messages, overly capitalized messages, mysterious links, hyperbole, and using aggressive language can make users suspicious of a message. With SPAM and phishing messages increasing many mobile phone users are on guard.

Provide clear opt-out instructions: If users do not understand how to opt-out (unsubscribe) from your messages, they may feel they have no choice but to contact their carrier to request the carrier block your messages. Be sure to provide the legal “Text STOP to Quit” language in your messages on occasion as a reminder.

For A2P traffic, you should almost always send via a shortcode: If you are sending application-to-person (A2P) traffic, the carriers in the country you are sending to may require that this traffic be sent from a shortcode or on occasion from a Toll-Free number. This way carriers can review your messaging use case in advance, and offer better delivery as a result.

If you are looking to build a mobile program or have questions about mobile deliverability please don’t hesitate to reach out to set up a free consultation with Smart As A Fox.