I don't understand. Is there something in the content of the message that is inadvertently causing AT&T SMS processing to croak? AT&T needs to fix that.

Do the incoming messages not conform to defined SMS standards? InReach needs to fix that.

Or is AT&T intentionally blocking specific messages? Regulators need to fix that.

I can see how AT&T would, and should, block incoming SMS messages from non-AT&T customers, unless this InReach thing has negotiated a special business contract with AT&T to accept the incoming messages.

But AT&T would have no cause to block outgoing SMS messages destined for AT&T customers. If the SMS message came into the AT&T system via legal and approved means, there should be no reason to not transmit it outgoing to the destination AT&T customers.