It depends on the context.
If it's my mother acknowledging receipt of a recipe, then it's fine.
If it's a co-worker acknowledging receipt of a legal document, then it is both unprofessional, and annoying.
I mock my co-workers by replying with an actual e-mail message with the word "Thumb!" in it. They've stopped thumbing my e-mail messages.
Disagree - a reaction is a perfect acknowledgement and a clear sign of “you don’t need to do anything here”. If they send an actual email it could be:
Acknowledged, thanks.
By the way can you change X to Y?
In the logic presented in this thread, how is an emoji any different from the word "Thumb?"
This is what we used to say back in high school.
When you have actual "real world" experience, you learn that while language changes, there is professional language that you use in the workplace, and there is informal language that you use in a bar.
You don't use a single vocabulary for every interaction in every situation of your life. You alter your speech for the situation. You don't talk to the cop that just pulled you over, or the bank manager you're trying to get money from, or your mom the same way you talk to your friends watching a sportsball game.
You mean like articulating complete sentences?