Google Email
Replying and Forwarding existing messages
You might want to response to some of the messages that you have in your Inbox. To do so you can use your Reply (just to the sender) and Reply All (respond to everybody in the original message) buttons from the message screen:
If you want to send messages to different audiences to the ones included in the original messages, you should use the Forward button:
You can even forward an entire conversation using the Forward all button from the right side of the conversation view:
