I know that in Gmail, I can normally find the IP address of a non-Gmail sender by going to "Show original" in a given message and then finding the IP address after the final "Received: from".
However, let's discuss a converse situation. If I send a message via Gmail, will the receiver be able to trace my IP address from that message? I have tested it out (e.g. sending a message via a Gmail account to another Gmail account I have), and could not trace any IP address besides that of "mr.google.com", which is the mail server's and not mine. And indeed, according to http://ask-leo.com/can_gmail_be_traced.h tml, mail sent from web-based mail services (like Gmail or Hotmail) originates on the service's server, not one's computer, such that one's IP address is normally not compromised (unless law enforcement is involved, which isn't likely if nothing illegal was done).
But I would like to be sure, for privacy reasons, that my IP address isn't shown if I send a message via Gmail. Any input from people who know about this stuff is welcome. Thanks.