Best wishes, kind regards or none of the above?

We used to sign off letters using "yours faithfully" or "yours sincerely", then email came along and it was all "kind regards" and "best wishes". Now, it seems, we hardly sign off at all. With so many forms of written communication- email, text, Twitter, What's App- what new etiquettes are emerging, and where are 'digital natives' simply getting it wrong? Emma Gannon is author of Ctrl, Alt, Delete: How I Grew Up Online, and hosts the podcast of the same name. Producer Sally Heaven.