The amount of ways to interact with people online has been increasing, and you probably use different and more chat and email applications now than ten years ago.
Emails are often kept for years, and are stored by your email-providers.
It's rather easy to look them up and find that old email that you now need again.
But what if you would be able to do more than just storing them?
You could have them clustered by topic, time, content, addressees,... in an automated manner.
You could see differences over time, or maybe analyse the way you write your emails.
Combining them with chat histories to have a detailed trail of interaction with your family and friends... maybe combine them with your social media interactions with them.
Or you might want to see how a current interaction with someone is similar to one from the past, and see if you want to do it differently this time.
All the content in the emails can be logically grouped and automatically tagged and classified: professional, medical, administrative, holidays, family,... or according to tone of voice, language,...
This huge source of personal information has the advantage that it probably reaches deeper into the past than any other datasource readily available.