Below you will find the steps for creating an archive/offline PST File within Outlook 2010. Retaining a large number of emails on the actual mail server can have a negative impact on your account's performance within Outlook and within the webmail client. By creating an offline archive, you can retain the files in the same mail profile while improving your account's performance within it.
To start, you will select File. Within the File menu, click on Account Settings to display the Account Settings drop-down menu, where you will select Account Settings to open the Account Settings dialog.
Within the Account Settings dialog, select the Data Files tab. Next, select the Add icon to open the New Outlook Data File dialog.
Within the Outlook Data File dialog, you will select Outlook data file (.pst) from Types of storage: then select OK to move forward to the next step.
Within the Create or Open Outlook Data File dialog, you will name the PST file you wish to create and select the location you wish to save it. After choosing the location and giving the file a name, select OK to create the file.
Note: By default, it generally opens to C:\Users\<User's name>\Documents\Outlook Files
After creating the PST file, you will be returned to the Account Settings dialog. You will notice that the newly created PST file is now listed. Select Close to exit the Account Settings dialog.
After creating your new PST File, you will notice that the file now appears within the mail navigation pane below your email account(s). Simply expand the carat down to view the pst file. You can now create folders to store/archive historical email correspondence you wish to retain offline. To move mail, all you have to do is select the messages then drag and drop them into the desired offline folder.