Do you use BT Smart Messaging’s HTTP API for sending and receiving 2 Way SMS Messages? Be aware that on the 8th of March they will be changing the IP Addresses that they send SMS replies from and you will need to make sure that your firewalls are allowing traffic from the following IP addresses:
35.179.86.76
35.177.58.33
35.176.82.123
3.10.189.121
35.179.83.122
35.178.42.39