I’m still a fan of email for this reason. Once someone sends me an email, the copy in my inbox is mine, and the sender can’t later hide it/take it back/etc.
If I could get banks to send me financial statements as PDFs in an email I would sign up in a second.
If it's really important to you, you can use one of the companies which receive and scan your post into emails. Then change your bank correspondence address to them.