There’s an email in your inbox. You read it.
You’ll reply in a minute or later or when you have the answer.
Reply – to the sender
Reply all – to the group – (Important distinction. Not everyone needs your reply)
These two options keep the very important thread of the conversation.
Replying with a new message – does not include the conversation – leaves the receiver confused.
Keeping the thread is a thoughtful effort that benefits both of you.