Need backup SMS alerts set up for when order emails fail to deliver

Our platform sends every important order update by email only, and that already causes problems: some messages bounce because an inbox is full, some providers reject mail from our address, and a few users mistype their address at registration. Each failure means a customer misses a status change, a dispute notice, or a payment confirmation before anyone notices the order has gone wrong.

I need a backup channel that sends an SMS automatically when an important email fails to deliver, without duplicating every message. Only a defined list of critical event types should trigger it, and the system must check the actual delivery result first, not just assume the email went through.

The key requirement is cost control: a daily limit per user, a monthly budget cap for the whole channel, and clear behaviour once a limit is hit (the event is logged, no SMS is sent). I also want an instant on/off setting that needs no code changes, plus a short report of sent messages and their cost.

What I expect from the contractor:
— SMS gateway API integration (provider to agree together)
— logic that reads email delivery status and decides when SMS fires
— a fixed whitelist of critical notification types
— daily and monthly spending limits with a warning near the threshold
— a compact report of sent messages and running cost