I pretty much want no marketing messages ("book your rental car for Singapore!" "You didn't book a rental car in Singapore yet!" Your flight is arriving in Singapore in ten minutes and you don't have a rental car reservation!!") but I do want informational messages (flight delays, boarding).

I only one those messages through one channel and not three, and as mentioned above they need to be reliable. There are gate agents who will trigger the "boarding has begun" message and then ten minutes later announce that there's a 30 minute delay they knew about an hour before the GA triggered the boarding message.

Similarly the estimated boarding time in the app should be updated more regularly when they know boarding is delayed.