SMS Deliverability

SMS can be an extraordinarily effective communications channel for marketing, sales, and service. When receiving an SMS, 90% of messages are read within 3 minutes of delivery. But its that last word, delivery, that is somewhat complicated and nuanced.

When sending a text through Prompt.io, we process that message through a Message Network Operator (MNO) such as Twilio, Telnyx, or Bandwidth. The MNOs typically route the messages to the appropriate carrier (ATT, Tmobile, Verizon) which in turn sends to the destination mobile phone.

Understanding Carrier Filtering

At the carrier level, content is often examined algorithmically to determine if the content is appropriate for delivery — this is known as "Carrier Filtering" or "Carrier Blocking." Over time, as SMS volumes and the number of bad actors have increased, the carriers have become much more aggressive in blocking outbound messages. The algorithms used by the carriers are not published and change frequently.

Message filtering can often be triggered by a simplistic list of static keywords or prohibited term. Advanced, adaptive machine learning systems are also employed that have a more dynamic approach.

Keywords to Avoid Filtering has been seen frequently with keywords such as COVID, Corona Virus, Loan, alcohol, payday, loan, and rebate, prize, sweepstakes. Apparently, these keywords represent frequent attack vectors for spam/phishing.

Improving Deliverability

Improving Link Deliverability If you are seeing carrier filtering based on a link that you are trying to deliver, Prompt.io can perhaps help by redirecting through the prompt.io domain, which has been whitelisted by carriers. Talk to your account manager about setting this up. For instance, say you are trying to get people to xyz.com — we could offer to set up prompt.io/l/xyz — that domain will not trigger carrier filtering because it is whitelisted and if customers click the link, it will get redirected to xyz.com.

Prompt.io offers "First Message" functionality to help facilitate improved deliverability. The first message will always be delivered to a contact immediatetly prior to delivery of the first content delivered to the recipient.

Detecting Deliverability Issues

For messages that are carrier filtered, very often the message will show a Carrier Filter error. In the case of Twilio as the MNO, that error code will show in Prompt.io as error 30007. Note that in some cases, the carriers will actually report a filtered message as delivered — and not report the error code.

Toll-Free Improves Deliverability

Use of toll-free numbers can show an increase in deliverability over use of standard 10-digit local channels, specially for high-volume sends.

MMS Deliverability

MMS, sendiing photos and videos, is a great way to connect and send content. Each carrier and MNO have different file sizes that are supported. Maximizing deliverability of MMS is built in to our platform — the message network operator limits as well as the carrier limitations are utilized to ensure best possible delivery. For video, it is recommended that files are compressed to no more than 500kb which is good for about 15 seconds of video.