Outlook stores email, calendar and contact data in a personal file folder format know as a personal storage file (.pst). These files are generally referred to as pst files. Below you will find the steps you would take to export your Outlook data to a .pst file within Outlook 2010 (Note: the process is the same for current versions of Outlook as well).
Select the File tab, Open and then Import from the Open options:
The Import and Export Wizard will then appear. Within the Import and Export Wizard, select Export to a file from the Choose an action to perform: options, then click Next.
Select Personal Folder File (.pst) from the Create a file of type: options, then click Next.
Click the top level folder that contains the messages you want to back up. For POP3 accounts, the top level folder will generally be titled Personal Folders. If the folder contains a subfolder that you want to include, select the Include Subfolders check box, and then click Next.
Under Save exported file as, click Browse and then specify a name (e.g. Mail Backup) and location for your backup file.
If you back up a .pst file that you have backed up to before, click one of the following:
Replace duplicates with items exported. - Existing data will be overwritten with the information in the file being exported.
Allow duplicate items to be created. - Existing data will not be overwritten, and duplicate information will be added to the backup file.
Do not export duplicate items. - Existing data will be kept, and the duplicate information in the folder will not be copied to the backup file.
After choosing your Option, naming the file and selecting a location to save it to, click Finish.
Next a box will appear that will allow you to name the file and assign a password. If you do not wish to password protect the file, leave the fields blank and select OK to complete the process.
Note: If you are backing up to a previously created .pst file, you will not see this prompt.
After completing the steps above, a box will appear that will track the export process. You will be unable to utilize Outlook while the export is running. The status box will disappear once the export has been completed.
Note: You will not have access to your email while the export is taking place.