1. Open your Outlook, click Distribution List you try to export.
And click File, Save As…
On the Save As window, select Text Only (*.txt) in the Save As Type drop down on the bottom.
Open the saved File in Microsoft Excel
|2. Open the saved file in Microsoft Excel and make sure the Files of Type should be All Files, or Text Files.
When you select the file from previous step, you will be automatically redirected to Text Import Wizard like the below.
Please make sure you select the right Start import at row. (In this case, the contacts begin at row 5.)
Save Excel file as CSV file
|3. In Excel, click File, Save As and on the Save As window, make sure you change the Save as Type as CSV.