To ensure your Outlook .pst file stays trim and doesn’t get bloated with old and outdated emails, configure its AutoArchive options so that older messages are automatically removed or filed away.
To do this, right click the folder to archive and choose Properties, AutoArchive tab and select the Archive this folder using these settings option. Now enable the Clean out items older than and set the appropriate time period. Only select to Permanently delete old items if you really don’t want them saved. Enable, instead, Move old items to default archive folder and Click Apply.
If you haven’t got AutoArchive configured to run periodically, you’ll get a warning to this effect and Outlook will set it to 14 days by default. You can change the timing by choosing Tools, Options, Other, AutoArchive.
Now, every 14 days (or when you specify), AutoArchive will run and the old items will be moved to your archive folder. Your archive file will appear in your folders list so you can drag and drop messages from it back into your regular Outlook folder if there are archived messages you need to refer to.