To create a backup file in Outlook, follow these steps:
1. Open Outlook and click on "File" in the top menu.
2. Select "Open & Export," then choose "Import/Export."
3. In the Import and Export Wizard, select "Export to a file" and click "Next."
4. Choose "Outlook Data File (.pst)" and click "Next."
5. Select the mail folder you want to back up and click "Next."
6. Choose a location to save the backup file and provide a name for it.
7. Click "Finish" and set a password if desired for added security.
Your Outlook data will be backed up to the specified .pst file.