A Guest in the Room
When you receive a genuine (not-spam) email from someone you know, do you assume it’s for you?
Of course you do — it’s addressed to you.
But is your name on the “To” line, the CC (Courtesy Copy) line, or the BCC (Blind Courtesy Copy) line?
If your email address is in the “To” line, you are the primary recipient. The sender is talking directly to you. Feel free to reply as appropriate.
If your email address is in the CC line or the BCC line, you are not the primary recipient. You have been copied or blind-copied because the sender wants you to be privy to the content but isn’t writing directly to you. You are like a guest in the room.
As such, email etiquette suggests that you consider whether a reply is appropriate. I recommend if you’re on the CC line, don’t reply. You’re on the CC line for a reason — only so you receive that information. Let the folks on the “to” line respond, unless you are specifically invited into the conversation.*
Before you click “Reply,” consider whether you are being asked to do so.