Microsoft has completed the acquisition of FrontBridge on August 31, 2005, and consequently integrated the company's technology into the Hosted Exchange email services. One of the core aspects of the FrontBridge technology was email protection against viruses and spam. According to a report from CRN, Microsoft's Hosted Exchange services have been blacklisted by several anti-spam websites. In fact, a non-delivery report (NDR) server for Exchange Hosted Services has found its way onto no less than three block lists.

Jay Vernon, director of client services for Exchange Hosted Services via e-mail revealed to CRN that the blockage is limited to non-delivery reports. "By design, we send NDR messages from separate servers than those routing e-mail. We do this because, when a customer is affected by a spoofing or directory harvest attack, a spike in NDR messages may result, thereby landing the NDR server on the block list. By segmenting the server roles, we ensure that legitimate email is delivered, while illegitimate NDR messages are blocked," Vernon explained.

According to Microsoft, despite the NDR incident, the actual service quality of the EHS has not been impacted. Vernon added that the customers are simply experiencing blocked NDR messages.

"The customer may have been spoofed, and when a spoofed message is rejected by EHS or the destination mail server, this NDR server routes an NDR message. The customer could perceive the increased volume of illegitimate NDR messages as a spike in spam messages," commented Vernon.