For me the digital key is very vital for the protection of emails and any document sending or receiving from any known or unknown users

For me the digital key is very vital for the protection of emails and any document sending or receiving from any known or unknown users.  For my company I would input in the policies and procedures that any email or document that pertains to the company must have a digital key attached to it.  As well, the public key must not be shared to anyone but the receiver.  I would have all digital key to be changed every 90 days.  This would reduce hackers to attached virus codes and if there were virus codes that would be a key tracing back to the sender.