The major carriers (AT&T, Verizon, Tmobile and Sprint) have aggressively increased their message filtering towards group messages/blasts containing URLs or pictures or unknown "trigger words" sent using local numbers.

Sprint and T-Mobile, in particular, have recently (Q2 2019) started aggressively filtering your messages, but they are not letting us know that the message was filtered. In other words, they are not sending a “blocked for carrier violation” error response to our servers.

Your message shows as delivered to Sprint and T-Mobile phones but you or your subscribers didn’t actually receive it. Our “delivered” status log is reported in real time, and hence, we are only reporting what Sprint and T-Mobile are sending or not sending.

This false reporting by T-Mobile and Sprint is a crude way to trick spammers into thinking they are being successful and to limit their ability to game the system. However, this is bad as we can’t accurately report the message status. You may think someone received a message as it shows as ‘delivered’ when, in fact, it wasn’t.


Inside the US solution (when sending 1 on 1 text messages that include links)

How to send a message from the Short Code
Using an AMC to send links from the Short Code

Free vs Paid Short Code Keywords

How to Set up and Use your Short Code Keyword

Organization Settings Page


Outside the US options

We have employed a number of workarounds in our system to help avoid the issues we are seeing.

Our Current Workarounds

Toll-free numbers (newest and most promising)

Secondary numbers

Redundancy – Multiple domain masking

Redundancy – Carrier reprocessing

Alternative options to using links

Our best recommendation now is along the secondary number route discussed above combined with a toll-free number. We think this is your best opportunity to send non-spammy, personalized bulk messages that would see the highest likelihood of making it through the current mobile carrier filtering changes.  

More information

Why do carriers have content and spam filters?

When subscribers receive messages they find objectionable, they may file complaints or report the carrier to governing bodies, seek damages or simply stop being a customer. All of these things reduce the revenue of or increase the costs for carriers. Thus, it is in the best interest of carriers to protect their subscribers from what they consider to be objectionable content.

How do carriers filter messages?

There is no standard practice for carrier filtering across all carriers. For some, filtering can range from a simple static list of prohibited terms to advanced, machine learning systems that work in real time. Regardless of the system, carriers keep their filtering systems closely guarded secrets. In turn, PastorsLine cannot say definitively how these systems work or why a particular message was filtered.

How do I know if my messages are being filtered?

PastorsLine does not always know or predict when a message has been filtered by a carrier. Some carriers falsely report filtered messages as 'delivered' to prevent spammers from reverse engineering filtering systems. In other cases, carriers will tell PastorsLine that a particular message has been filtered.

How do I prevent my messages from being filtered?

If you see an increase in carrier filtering of your messages, these questions provide some general guidelines for sending messages:

  • Is it a good user experience?

A confusing message to users might seem like someone they don’t know has their contact information. Suspicious users are more likely to report messages to their carrier, and when messages are reported to carriers, it becomes very likely that future messages from that number or with similar content will be filtered. In some cases, the user may have forgotten that they requested the message. Also, how the message is formatted and written is important: overly long messages, overly capitalized messages, mysterious links, hyperbole, and using aggressive language can raise the level of suspicion users feel about a message.

  • Do users have clear opt out instructions?

If users do not understand how to opt out, they may feel they have no choice but to contact their carrier to request that these messages are blocked.

  • Is a single number being overworked?

In countries where rate-based filtering takes place, sending too many messages from a single phone number or alpha sender ID during a time period could cause that phone number or sender ID to be blacklisted.

United States and Canada filtering

Filtering Mechanisms

Carriers in the U.S. and Canada appear to be using adaptive (machine learning) software systems to protect their users. These systems take into account both the rate of send, as well as the content of the messages, and behave very much like email filtering systems. Messages receive a cumulative score based on how many messages have come from a phone number during a time period, how many similar messages have transited the carrier’s network or if the message contains content that makes it a high match for spam. Time periods are measured by the second, minute, hour, and day.

PastorsLine does not definitively know how many messages can be sent from a long code before a user can expect to hit a filter. However, we highly recommend following the guidelines mentioned in Messaging Principals and Basic Practices published by CTIA in Jan. 2017, where CTIA suggests that Application-To-Peer (A2P) Messaging that’s “consistent with typical human operation” should be expected to be deliverable across the messaging ecosystem. Some key attributes of typical human operation include:

Carriers in the US sometimes report to PastorsLine when a message has been filtered. If you suddenly see that a large number of your messages are resulting in a status of “Undelivered” with a 30007 error, the carrier has taken some sort of action which has caused your message to be filtered.

Message Delivery in the United States and Canada

I think my number has been blacklisted by a carrier. Can I get it removed from the blacklist?

No. However most blacklists in the US and Canada use a “cooling off” period, which means that most numbers will automatically be removed from the blacklist after a period of time. This period of time varies based on how many messages were blocked by the carrier from this number, and carriers do not share this time period with us.

Can I get my messages whitelisted by the carriers?

US Carriers do not whitelist messages from long code numbers. Short codes are essentially numbers which have been whitelisted for a particular type of pre-approved traffic. If you are sending many messages with identical content to a large number of users, you are at a high risk of having your messages filtered by carriers and should consider a short code.

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