Click “Option” under the “File” tab.

Click “Open & Export in the left menu and then "Import/Export".

Select “Export to a file,” click Next.
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Within the Create a file type: select "Comma Separated Values" which is a CSV file, click Next.
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Under “Select folder to export from,” select the contact folder that you want to export, and then click Next.

Choose a location and name for your backup file and then select Finish.
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You can click here for importing instructions.