Traditional methods of business communication tend to mean paper-based messages such as formal letters, brochures, reports, proposals, and notes.
There is no denying the fact that digital communication has a lot more advantages as compared to the traditional methods of business communication, but there are certain cases and situations where traditional methods and preferred over digital communication.
Paper-based messages provide objective evidence that a formal undertaking has been issued. The advantage of paper-based messages is that they can't be tampered with and not reproduced. They represent the signature of the concerned authority and are always treated above the digital signatures.