A project team is working on a sensitive project that requires the use of an isolated email system for all project communications. Outside vendors are frustrated by the lack of response to emails sent to the corporate email addresses of the project team. Which of the following is the BEST way for the project team to communicate with outside vendors?

A. Invite the vendors to utilize the isolated email system.
B. Use a public email system for external communication.
C. Request the vendors use a courier to deliver project documents.
D. Provide the vendors with a phone roster to set up regular meetings.