The Value of Email
It is simply not enough to only keep a copy of the final signed contract. The correspondence leading up the final document is of immense value and in a dispute can clarify an issue swiftly. In a he said/she said situation, having the written correspondence leading up to the problem at hand will bring about a quick resolution to the problem.
For that reason, and many more, email is a business tool that will stand by you and will keep you connected to your company, your clients, your suppliers, your employees, etc ... in good times and in bad times.
I have always been the company 'vault'. I quietly filed away everything that came to me and my bosses (even in cc) by email. It soon became common knowledge that if any issues came about, others in the company could rely on us to have a copy of the threads of correspondence. Employees (at all levels) soon learned the value of keeping their correspondence close at hand and rather than continue to come to us for help, they soon curated and organized their email accounts. Having to admit to the President that you had not kept valuable correspondence close at hand, not twice but three times ... well, you understand ...
To that end, I advocate keeping email correspondence as long as possible, certain as long as legally necessary. I further organize my clients by doing a mass archiving at the end of the calendar year (much like I did with my paper filing systems). If your system is set up properly this archiving requires little effort, takes no time whatsoever and your documents are still close at hand but not cluttering up your current system.
There is certainly more to a productive and efficient email account that just this 'filing cabinet' ... the processing of emails adds another dynamic and another layer to the system. This part of email organization is more individual, and should be custom-built depending on your way of working and the type of work you do. Rest assured, it is easily tackled and set up either by yourself, your assistant, or an email and calendar management specialist.