Email address geolocation is the process of geolocating newsletter subscribers when they open an email. Email address geolocation is made at ESP level by the way of IP address geolocation.
The process has some limits and become more complex whith emails being more and more often opened on mobile devices. Email address locations are used when no other location data are available.
After email address geolocation, newsletters can be segmented end personalized based on location. Email address locations may also be used to optimize sending times.
An example of email geolocation report offered by british ESP Pure360: