teneros.JPGAccording to a research report cited by Mountain View-based Teneros, the average business experiences seven hours of email downtime each year.

Can you survive without your email? Apparently those businesses can’t, and they hire firms like Teneros to provide “application continuity” for Microsoft Exchange, the software back-end behind the email systems of most corporations.

The product itself is a plug-in appliance, the Application Continuity Appliance (ACA) that kicks in within moments of a system failure, keeping the network moving until it can be repaired.

Teneros launched the ACA in August 2005, and appears to have made good headway since against more expensive competing options. It’s generally used by small- to medium-sized businesses.

The $40 million financing was led by Advanced Equities, with participation from previous investors Goldman Sachs, New Enterprise Associates, Sevin Rosen Funds and Star Ventures. It was Teneros’s fourth funding so far; the company has now raised a total of $84.5 million.