Corporate security controls are needed to collaborate with external business partners and customers as noted in the article below:
Corporate Collaboration – Secure Controls needed beyond the firewall
QUOTE: Secure collaboration tools have made it easier and safer to share large files and sensitive data safely. Sharepoint and file servers are just two of the many ways employees can collaborate within the company without exposing data to theft or loss. That level of security appears to stop at the firewall, according to a recent cloud survey commissioned by IntraLinks and conducted by Harris Interactive. A significant number of employees were using email and other insecure methods to send and receive large files and sensitive information with partners outside the company, the survey found.