Same SMS messages always fail to be received


    Hello. I work for a company that builds white label chatbots for financial institutions. One of the channels we offer the service on is SMS, leveraging twilio as our provider to enable delivery of SMS messages.


    I use my T-Mobile phone for receipt of inbound messages to test and demonstrate our technology. Recently, I'm experiencing behavior where the same exact messages in specific multi-part conversations will fail to reach my phone. Looking at twilio's SMS logs for these undelivered messages, they show a status of delivered to the carrier network (in this case that's T-Mobile).


    I asked another individual with T-Mobile to test as well and he experienced the same behavior (same missing messages). But my colleagues with other carriers are able to receive all the messages on their phones without issue. One additional note is that if I modify the text in the missing messages to remove certain key words or phrases, those new messages WILL be delivered to my phone successfully on a subsequent attempt. If I restore the text to the 'undeliverable' version, it will fail to reach my phone again. So at this point it appears something internally on T-Mobile's end is preventing delivery of very specific messages in a 100% reproducible way. Spam blocker has already been disabled for my account, and customer support has been adamant that there's nothing else which which would prevent messages from being delivered.


    I've spoken to multiple T-Mobile technical experts about this issue and opened at least a couple support tickets. I've received automated texts telling me the issue is resolved but no personal follow-up from any technical contacts at T-Mobile, and unsurprisingly the issue is not resolved.


    At this point I'm reaching out on behalf of myself personally (As a customer/recipient, I wonder why I can't whitelist all messages from a specific number regardless of what internal anti-spam countermeasures that number might be triggering)... and on behalf of my company (As a legitimate service delivering messages on behalf of established, FDIC-insured financial institutions, we'd like to better understand the reason specific messages might not be delivered to mobile end users).


    I've offered additional details and availability for joint troubleshooting to T-Mobile support. I can provide the originating phone number, my (inbound) T-mobile number, message SIDs, timestamps, and precise text for the missing messages. I'd hope all that information could enable you to to find some logs on the missing messages and determine a root cause. This issue is impacting me negatively on multiple fronts. I'd appreciate any assistance.

      All replies

      • tmo_mike_c

        We totally wanna help you as best as we can. What's the short code your messages are coming from? Has this messaging service ever worked before? Are you able to get texts from phone numbers? I suggest removing unique characters like symbols from the message and testing it again if you can. Sometimes unique characters may keep messages from being received.

          • magenta8601732

            Thanks for the reply tmo_mike_c.


            1. We don't have a short-code registered for the particular account sending these messages. The phone number sending the messages to my device is 3212046243.


            2. The messaging service has worked for as long as I can remember. Messages sent via Twilio using this phone number are received 100% of the time by my colleagues and were being received 100% of the time by me up until May 6. As of May 6, I still receive the majority of messages sent to me. But very specific messages are predictably and repeatably not received, despite being shown as 'delivered to carrier' on Twilio's end.


            3. As best I can tell, I receive all other texts just fine. But realistically, in general personal use I'd have no way to really know if a single message isn't received.


            4. There are no unique characters or symbols in the blocked message (aside from maybe an exclamation point), but there are definitely words or phrases I could see being blocked as part of a SPAM filter if there was suspicion of an illegitimate message source.


            This is the message that IS NOT received by my T-Mobile device:

            Great news! You're eligible for the Premium Visa Platinum Card and for big annual savings. You can view complete credit card terms & conditions here: (link to T&C page)

            Twilio Message SID for an occurrence of this message: SMf006c9836b2c61f543f362b0845357cd


            If I update the copy as follows, this message IS delivered to my T-Mobile device successfully:

            It looks like you're eligible for a new card with big annual savings. You can view complete terms & conditions here: (same link to T&C page)

            Twilio Message SID for an occurrence of this message: SMb5fbc239b4c9c5a98c5cbea20af1bdda


            Potential objectionable words/phrases I removed to ensure successful delivery:

            Great news!

            Premium Visa Platinum Card

            credit card


            It would be great to understand why the top message cannot be delivered successfully and whether or not, as an end-user on the receiving end of these messages, I can white label the phone number to ensure all messages are received successfully. I've included a representative Message SID for both cases above. Hopefully that can help identify why they're handled differently. And to reiterate, prior to May 6, the top message was being delivered successfully from the same originating number to my T-Mobile phone... so not sure what changed.


            Thanks again.

          • tmo_mike_c

            Hi again.


            Have you tried the steps in my previous post? Please let us know. Thanks.

            • magenta8601732

              @tmo_mike_c when I send the same message to myself via gmail using, the entire message is delivered successfully.

              • magenta8601732
                • magenta8601732

                  tmo_mike_c @


                  I didn't have to change the language at all for gmail. I'm revisiting this now because I'm experiencing the same issue across other messages.


                  Here is another sample message being generated by our platform and sent to T-Mobile via Twilio which it appears T-Mobile is not handling well:

                  For CREDIT CARD xxxx7834:




                  • Current balance: $0.00



                  • Available Credit: $7,500.00



                  • Credit Limit: $7,500.00


                  Would you like to see recent transactions for this account?


                  This message never got delivered to my device, but Twilio shows 'Delivered' in the 'Carrier Network' Stage of their logs.



                  The same exact message, sent the same exact way, is delivered without issue by AT&T (as one point of comparison).


                  It's worth reinforcing that I am approaching this problem from 2 perspectives:

                  1. As a T-Mobile customer, I want to ensure I am receiving all the messages which are sent to my device.

                  2. As a representative of a business that delivers messages to T-Mobile customers, I want to ensure that delivery status of those messages is reflected accurately... and to understand what steps can be taken on our end to ensure successful delivery.


                  I would really appreciate the opportunity to speak with somebody by phone regarding this issue. As mentioned in my previous post, I opened multiple support tickets when this first occurred and had disappointing interactions / poor follow-through from multiple T-Mobile Experts. I can reproduce in real-time, provide phone numbers, message sIDs, etc... anything to help identify the root cause and work toward a solution.


                  Right now we're re-evaluating OCS2 vs GSM message encoding and the impact that certain characters may have on deliverability via T-Mobile. But it would be great if someone there could provide guidance or knowledge of any known issues.

                    • tmo_mike_c

                      You've been really thorough with your troubleshooting and I appreciate that. I'm bummed this is still going  on, but I agree you'll need to speak with our Tech Care team and revisit those tickets with these new examples. You can Contact Us and call, or you can message our T-Force team through the Facebook and Twitter links. Either way, I'd suggest mentioning those previous tickets and having these examples on standby so they can update the ticket with them.