Simply select the "Clients Tab" on the left hand side.

In the top right corner you will click on the three dots.

A list of three options will appear at the bottom of the page. Select "export client list" and it will download a .CSV file to your computer.

You can then add this file to your chosen address book application or open it with a program like Microsoft Excel or Apple's Numbers and from there you can copy and paste any part or all of the list directly to an email.