I've saved many letters over the years, and when I look at them again they bring the letter-writer right back into my mind, even those who have passed on. When I see my mother's handwriting, I can hear her voice. When I read a friend's letter, I can picture as she was back at the time when she wrote it.
When I was growing up, it was a thrill to get a letter in the mail addressed to me. I still feel that way. I love actual cards, be they birthday, Christmas or whatever, much better than ecards. I can put a real, paper card on the mantle and enjoy it every time I look in that direction. While emails can be saved (and I do save certain ones), it is not the same. They are hidden away. And most people delete their emails as soon as they have read them.
Handwritten letters and cards often contain family and friendship history. Years later letters can be discovered by future generations that will tell them something about the past. But no one is going to look through ancient emails, even if by some chance years from now they could still be read by future computers and electronic devices.
I have letters from my mother dating back to when I first moved away from home. I have letters from my husband written to me before we were married. I even have a letter from an author of a series of favorite books that I read when I was growing up.
My grandmother saved her correspondence, and there is a "letter" from me written when I was very young, before I could actually write. It looks like a row of ocean waves. But I was trying!
Of course, there are stashes of Valentine's and Mother's Day cards that I gave my mother when I was growing up and that my daughter gave to me.
Emails and such are fun, but handwritten cards and letters are pure gold.