In-place archiving provides an additional mailbox that allows you to store messages online rather than in local PST files. Once activated, it will archive messages 2 years old or more. You can also move or copy messages manually by dragging them from your regular mailbox, set up rules to move messages or import messages from existing PST files.
To have in-place archiving set up, contact your departmental IT support person to request it.
A more detailed description of in-place archiving can be found on Microsoft’s website.