Far too many.
People send messages to ask you a question. To request information. To share an opinion.
And the other person is left hanging every minute you don’t reply.
You can’t respond to every message straightaway.
But you can acknowledge that you’ve received the message and when you’ll get back to them with a proper response.
So for your most important stakeholders, please reply within max. 3 hours.
Don’t leave them hanging.