Here's how toexport your contacts from your Roundcube webmail so you can use them in other email programs.
Login into webmail at https://webmail.yourdomain.com (replacing 'yourdomain' with your email domain name).
1. Click on Contacts on the left.
2. Click on the > arrow next to Export button that is on the right.
3. Click Export All.
This will need to be done for each email user individually.
*This method exports all contacts as one (multiple contact) vcard. This multiple vcard file can be imported into Gmail, and it can then exported as a csv file, which is required to import them into Outlook.