> 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.
Whenever I book a flight google offers to set alarms and gives me don't forget your flight tomorrow notifications. They are obviously reading the email to achieve this.
https://policies.google.com/terms?hl=en
> 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.