You might want to export your list of contacts for import to another program or just to save a backup copy on your desktop. Whatever the reason, here are the simple and easy steps.
Within RoundCube, click on the Address icon (upper right). From the list, select the contacts you want to export. Click on the Export icon (top left). You'll need to decide the format of the exported file. The format will depend on how you want to use the information.
Within Horde, select the Address Book icon from the navigation bar. On the next screen, select the Import/Export icon. On the next screen, look for the section "Export Address Book." Choose the export format. Since Horde lets you have more than one Address Book, select the Address Book you want to export and click the Export link.
Within SquirrelMail, click on Addressses. On the next screen, near the bottom you'll see "Address book export." Select your Field delimiter from the list or type in a Custom field delimiter.