Any email is traceable to the IP address of its sender. Gmail, the online email system owned by Google, is no different to any other email system in this respect, as Gmail has to follow the conventions of email protocols and network communications. However, it is not possible for most users to find the IP address of a Gmail account holder.
An IP address is a unique identifier for a computer connected to the Internet. Without an IP address no computer can receive data over the Internet. Communication follows the "client-server" model where a client sends a request for a resource and receives back a response from the server. The two messages are not linked, and so the message from the client has to contain its IP address so the server knows where to send the response.
Gmail IP Address
Gmail account holders access their accounts through the Gmail Web page. Other email systems require emails to be downloaded into an email client program on the user's computer. However, with Gmail, that email client is resident on a computer owned by Google. Email servers sending an email to a Gmail account have to know the IP address of thre Gmail mail server, in turn, the Gmail mail server has to know the IP address of the Gmail mail client, but no one in the chain needs to know the IP address of the computer the user uses to read Gmail.
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Gmail does not log a user's IP address on registration. This is because a user might log in from any location to read emails, and registering an IP address for each user, restricting access to that account only from that IP address would reduce the popularity of the system. Therefore, Gmail does not hold anyone's IP address against their account. No one can discover any user details of a Gmail account unless the account holder volunteers that information.
Email IP Address
The header of an email contains a from email address and a to email address, a second and third address fields for CC and BCC and a subject field. However, the full headers of an email show a lot more information about an emails journey than is immediately visible on the received email. The receiver of an email can opt to view full headers and there they will see the journey of the email from sender to receiver, with the IP addresses of all the servers the email passed through and also the IP address from which the user entered the email text into the Gmail system.
User's IP Address
The account holder of a Gmail account should not worry too much if his IP address appears in the full headers of every email he sends. Most Internet service providers do not allocate a permanent IP address to their customers, but allocate an address from a pool of addresses they own. Therefore, the receiver of a Gmail email can only detect the Internet service provider that originated the email, and not the computer of the individual that sent it.