Por seguridad, Gmail no revela las Ip's de quienes te envían un mail.
Protecting our users' privacy is something we take very seriously. Personal information, including someone's exact location, can be gathered from someone's IP address, so Gmail doesn't reveal this information in outgoing mail headers. This prevents recipients from being able to track our users, or uncover what may be potentially sensitive personal information.
Y si revisas los headers de los e-mails que te llegan, dando en "más opciones" y después "mostrar original", verás sólo las IP's de los servidores, no la del remitente.
Salu2