To backup your email you may do the following:
On your outlook, click on File > Import and Export > Click on Export to a file > Personal File Folder (.pst) > Select which account (eg. Personal Folder. If you have multiple account, it would be best to export them) you wish to backup and click on Include subfolders > Then click on browse and select Desktop (so that the file exported will be on desktop).
After you have finish exporting, on outlook do the following:
In Microsoft Outlook, from the E-mail Accounts menu, select Tools. On the E-mail Accounts wizard window, select Add a new e-mail account, and then click Next. On the Server Type page, make sure to choose “IMAP” as the server type and then click Next. On the Internet E-mail Settings window, enter your information as follows:
Username and Email address: firstname.lastname@example.org
Incoming mail server (IMAP) and Outgoing mail server (SMTP): mail.apc.sg
After you are done, Click More Settings. On the Internet E-mail Settings window, go to the Outgoing Server tab. Select My outgoing server (SMTP) requires authentication. Click on Advance tab, change the Incoming server (IMAP) to 143 and Click OK.
Click Next. (when you see the email account page, where you key in the username and password earlier) Click Finish. (when it shows you congratulations)
** (If you have exported multiple .pst file earlier do repeat this step) On your outlook, click on File > Import and Export > Click on Import from another program or file > Choose Personal Folder File (.pst), Click Browse and choose Desktop (where you exported earlier) select the pst file > Under Select the folder to import from, click Personal Folders, select the Include subfolders option in the check box then click Finish > Click OK when you receive the following message: You are importing data to a location that does not fully support Unicode. To avoid loss of multilingual data, it is recommended that you choose a location that supports Unicode, such as a Microsoft Office Outlook Personal Folders File.Click OK to continue with the chosen location.