Does anyone even write letters any more, except for the official ones that arrive in brown envelopes and usually mean money - sadly going out more often than coming in, at least in my house?
I remember being taught in school the correct use of salutations and endings - Dear Sirs - standard for a business letter, yours faithfully if you didn't know the name of the recipient, yours sincerely if you did and had used it.
I haven't written one of those for a very long time.
I've just finished reading two books where the story depended on letters. In both case love letters. One was the classic discovery of the faded and scented bundle, written in coloured ink, tied with a ribbon. The second, more contemporary, featuring a relationship that began with two pen pals and moved on from there. Before reading the book I would have questioned if that was still a thing, but now there are sites that will put you in touch with people to write to - I just Googled it.
I am wondering though if that classic, the bundle of letters, will survive modern methods of communication? A bundle of printed e-mails, texts, DMs? Doesn't have the same romance - and is it likely? You might save a special e-mail, but a whole correspondence? Will this invaluable plot device recede further and further into the past?
And it is romantic. The keeping of the letters in the first place, their survival, sometimes a question over the identity of one or both of the recipients. Some classic novels are themselves a series of letters - epistolary novels - although they often contain diary entries and other fragments. These days their place is taken by those e-mails or even voice recordings. as in Janice Hallet's The Twyford Code.
Authors are finding new ways of using a favourite trope/plot device. But somehow it doesn't have quite the frisson of that shoe box full of letters.