Archiving mail in Mac OS X Mail is quite simple.  First, select the mail items you wish to archive.  Individual folders will not work for this process, mail within folders must be selected.  Then, select Message -> Archive (as shown).

Archives should be stored locally. They tend to get corrupted when you access them from a network folder. However, your local workstation/laptop isn't being backed up. So, you should backup the archive to secondary media, like a network folder or USB key, in case of a hard drive crash.

Seeing that Outlook allows for automatic and manual archiving, it only makes sense that it can also open an archive file.  To do so, select File, then Open, then Open Outlook Data File.

In the Open Outlook Data File window (which defaults to the My Documents\Outlook Files folder), select the data file you wish to open (archive in this case) and click OK.

Outlook has the ability to archive email to a local file.  This allows for decreased email load on the server (thus, a reduction of Inbox size) and for easy transfer of older mail between computers.  While Archiving runs, you may notice Outlook become less responsive during the process.  Once complete, response times should return to normal.

Outlook has the ability to automatically archive email to a local file.  This allows for decreased email load on the mail server (thus, a reduction of Inbox size) and for easy transfer of older mail between computers.  When starting AutoArchiving for the first time, you may notice Outlook become less responsive while the initial archive process runs.  After the initial run, there should be less email to process and response times should return to normal.