On the matter of keeping correspondence
I know many people just use their mobile devices for reading and sending emails. It tends to create a lazy approach to handling emails.
From many years of working in the engineering and project management fields, I know the value of an email, especially if there is a dispute. if one has the facts in an email, ites better than someones memory or opinion.
I happen to use a desktop computer (how ancient) so manipulating emails is a lot easier than a handheld device. It also means that my emails are stored on a local storage so I am not limited as to how much I can store if I were using the cloud. (I also make regular backups)
I have separate folders for different topics and file EVERY email I receive or send in the correct folder.
This practice has saved my behind a number of times.