I enjoyed reading the back-and-forth here in the thread, and I especially like the point about considering the depth of the response and how specifically it fit with the sender’s question.
Something I find unconscionably rude is a scenario
Student sends detailed email with multiple questions.
I take the time to craft a specific, point-by-point response that addresses each part of the student’s question, along with stat examples and/or code (I teach Data Science)
30 mins later student writes ANOTHER detailed series of questions, with a new subject line and NO acknowledgement of my previous answers.
I’m not even necessarily going for a ‘thank you’ here - even a ‘got it’ would go a long way. This isn’t the right way to behave with anyone - peer, senior, or subordinate.
My way of handling this is to simultaneously teach some manners and pump the brakes on the exchange. I ask them to clarify whether they received the first one, mention that i can check with IT if there might be a problem with messages going through, etc. and then wait for that response before diving into the next round.