Press Release

POSTINI EXPANDS MARKET LEADERSHIP THROUGH ACCELERATED INNOVATION, PRODUCT EXPANSION, AND GLOBAL CUSTOMER GROWTH

Integrated Message Management Leader Deepens Strategic Partnerships, Adds New Domestic and Global Customers, and Continues Its Profitability In 2005

SAN CARLOS, CA, January 17, 2006 — Postini, the global leader in Integrated Message Management, today announced that its market momentum continues to grow, highlighted by its expanding service offerings. In 2005, Postini delivered a comprehensive suite of message management services that extend Postini's offering beyond email security to instant messaging (IM), archiving and encryption. The company again demonstrated strong financial performance in 2005, with continued quarter over quarter revenue growth, a second consecutive year of profitability and positive cash from operations.

"2005 was the year of the product for Postini. Our steady success stemmed from the introduction of innovative new services," said Quentin Gallivan, who was appointed Postini's president and chief executive officer in November. "We will continue to bring new solutions to market this year that will enable companies to efficiently manage and secure their corporate messaging infrastructure. Postini's Integrated Message Management services provide the enterprise a way to seamlessly consolidate security, compliance, availability, and visibility for email and IM, with the ease of deployment that only a managed service can offer."

Postini, one of the largest independent managed email security services providers, processed more than 150 billion email messages in 2005, a 60-percent increase over the previous year. At the same time, customers continued to demonstrate a high rate of satisfaction with Postini's services as evidenced by the company's historically high rates of renewals and customer satisfaction, both in excess of 95 percent. New customers signed in 2005 included major global brands representing banks, legal firms, brokerage houses, pharmaceutical companies, consulting firms, chemical makers, retailers, and industrial manufacturers.

During 2005, Postini unveiled new products that reinforced its market leadership. Chief among these products are:

• Postini Integrated Message Management — a suite of message management applications that tightly integrates security, compliance, availability, and visibility technologies onto a single platform.
• Postini Archive Manager, a secure managed service that allows policy-based capture, storage, discovery and deletion of email and IM traffic.
• Postini Perimeter Manager for IM, for managing and securing instant messaging traffic in the enterprise.
• Postini Perimeter Manager — Small Business Edition, which provides an email security service specifically designed for small and mid-size businesses.

Along with these key service introductions, Postini has also achieved several milestones that further underscore its market dominance. These include:

• Expanded global footprint with the addition of European data centers in the United Kingdom, the Netherlands and Switzerland, and sales and support offices in London and Zurich.
• Listed in the leader quadrant in Gartner's email security boundary first half 2005 magic quadrant.
• Rated as the top information security vendor in TheInfoPro's customer satisfaction study of North American Fortune 1000 corporate users and information technology professionals. Postini outperformed all of the other information security companies in the study, including several high-profile and established security brands.
• Extended partnership with Trend Micro to license Postini's award-winning Postini Anti-Spam Engine (PASE), the content heuristics component of Postini's managed service infrastructure.
• Signed McAfee as a strategic partner.

About Postini
Postini is the global leader in Integrated Message Management, providing compliance, security, availability, and visibility solutions for corporate email and instant messaging. Postini offers a complete suite of services including message archiving and discovery, spam and virus blocking, and messaging continuity. The company's powerful managed services infrastructure seamlessly integrates with customers' infrastructure, providing uncompromising security for more companies than any other provider in the world. Postini's services protect organizations from a wide range of threats, reduce compliance and legal risks, ensure reliable communications, and enable the intelligent management and enforcement of enterprise policies that protect companies' intellectual property, reputations and business relationships. For more information contact Postini at 866-767-8461, or visit http://www.postini.com.