Google has updated its terms of service and explain to uses how it scans their emails to create targeted ads. The new terms and conditions explain more explicitly the manner in which Google software scans users' emails, both when messages are stored on Google's servers and when they are in transit.
Users of Google's Gmail email service have accused the company of violating federal and state privacy and wiretapping laws by scanning their messages so it could compile secret profiles and target advertising. Google has argued that users implicitly consented to its activity, recognising it as part of the email delivery process. It has done fairly well in court so far. Last month, a US judge decided not to combine several lawsuits that accused Google of violating the privacy rights of hundreds of millions of email users into a single class action.
Google's updated terms of service added a paragraph stating that "our automated systems analyze your content (including emails) to provide you personally relevant product features, such as customized search results, tailored advertising, and spam and malware detection. This analysis occurs as the content is sent, received, and when it is stored.
That clears that up then. If you don’t want any machine reading your mail, then you should use another mail service.