Individuals and businesses can use various methods to back up their email.

 

You're probably utilizing an Exchange or IMAP account if you use email for business. Your email is automatically archived by Exchange and IMAP servers so that you can view it from anywhere at any time. If you have an Exchange account, ask your administrator how to access your old emails. 

If you want to back up the message folders locally (in addition to maintaining them on the server), you can use AutoArchive to relocate or remove older things automatically, or you can export the items to an a.pst file that you can restore and use later.