Diary, Datebook, Ledger: Email is your Historical Record.
My mother spent many months poring over those letters. Both the revelations of family history, and the minutiae of how her aunt had spent the days fascinated her. She said she wished she had been a more diligent letter-writer -- that some historical record had been formed of her years besides photographs.
At that moment, and during many others over the years, I was happy I started archiving my email in 1995. I reflect from time to time on what kind of record those archives are forming. The personal correspondence varies from brief "want to grab dinner?"s to multi-page ramblings; notices of births and photos and links to sites and pages that have long since been shut down.
In recent years, it's also become a chronicle of many more details. As more services, online and off, send email confirmations, patterns emerge -- what I buy, where I travel, my interests, the wisdom of the day. I get emails about restaurant reservations, clothing purchases, newsletters chronicling milestones for my baby. Imagine finding a cache of papers detailing how they thought babies should be raised at the turn of the century, how much your ancestors spent on items from the Sears Roebuck catalog (surely the Amazon.com of their day) or the restaurants they dined at.
Will anyone ever go back through these archives? I don't know. (I might end up deleting years of the most cringe-worthy material if I did.) The immediacy of a box of paper, versus files on a hard drive, is certainly undeniable. On the other hand, it's far easier to search email!
Do you keep your old email? Do you expect anyone besides you will ever read it?
If you don't keep an archive of your mail, but you wish you did, check out Mailstore Archive.