I am designing communication system that will be sending targeted based SMS (ads/offers) to its customer. The basic system with low load scenario works well, and the SMS sent are based on an event like a person visiting a place, he should get all the promotions done by that store or stores near him based on his interest.
But this use case changes with bulk messaging for the holiday season. Although we can subset user interest vs the number of destination and can send a bulk message using an SMS sending API with 1000 destination.
This going to reach 5 million. How should I scale my system to communicate with the SMS sending API for this quantity of load.