Bad Information Behavior
Information systems can confirm that a message has been delivered, but they cannot confirm that a message has been understood.
That's less than half the battle
People send or forward messages in the name of communication, but that is more like narrow casting. You have no idea if the message is being read let alone understood.
"But I sent you an email," is not a good way to minimize your responsibility to communicate effectively.
You need to do more to follow up too. Automated reminders don't really help the situation either. They just add to information clutter.