Open SAGE and click on the customer list.
Click on Reports.
Click on Customer Details Reports (folder on the left) and select Customer Record CSV (Extended)
This will open SAGE's filter panel. Just click ok.
This will show you the Report.
Click on Export.
Choose where you want to save the file (I prefer the desktop). Then select the drop down 'Save as type'
Choose CSV Files (*.csv)
Click to save this file to your desktop.