Many of the telco providers have 'improved' their spam detection and have now required I do workarounds.
A few tweaks that made a difference:
1) Called one provider and got them to whitelist a few numbers (in my case Telus). amazingly quick at it but we are a larger user and it was stricly internal messaging and I provided a log of 10,000 outgoing recent samples.
2) Other providers (rogers and a couple... sucked). Users would need to call in and have that number whitelisted to their device. Doable as our use case here is internal
3) Variable data is your friend: by inserting variables to change messaging this made a real difference (Hi <fname> you have a lead from <provider> with the name <first_name> <last_name> that came in at <lead_time>. Respond by clicking <variable url link>
4) Frequency - if can be dialed down, good idea
5) Variable numbers - we use a pool of numbers where necessary so second message may be originating from different number
6) Heating up the number - get numbers in use, though not heavy for awhile before dialing it up
7) If possible, have the recipient reply back with basically 'any message'. Indicates interaction to the telco.
We do hundreds of thousands of outgoing/incoming sms messages using long codes per year and above are some of my best practices.
Sorry also with outgoing 'Stir/Shaken' mentioned earlier is another key. We use twilio for our messaging and implement this as well and the 'Trust Hub'
We build our own in-house communications both internal and external and between twilio and telnyx managed to work out most of the kinks. More then likely any 3rd party is using twilio anyways, so shouldn't be news to them if you are having issues and how they should go about fixing them.
Help combat unlawful robocalls and improve your call answer rate with SHAKEN/STIR—a fraud fighting protocol mandated by the FCC. Becoming a verified caller is simple, and helps fight against fraudulent calling and caller ID spoofing.
www.twilio.com
*bit of info.