Siebel Systems and Tumbleweed Announce Strategic Software Alliance

Industry Leaders Team to Jointly Offer Secure eMail Response and Web Service

REDWOOD CITY, CA - December 5, 2000 - Siebel Systems, Inc. (Nasdaq: SEBL), the world's leading provider of eBusiness applications software, and Tumbleweed® Communications Corp. (Nasdaq:TMWD), a leading provider of secure Internet messaging services, today announced that Siebel Systems and Tumbleweed have entered into a strategic alliance to integrate Siebel eMail Response™, Siebel eService™, and Tumbleweed Integrated Messaging Exchange™ (IME™) to provide a secure two-way communications channel to enhance customer response management and customer service on the Internet. The companies will jointly market and sell the integrated solution to organizations in financial services, insurance, healthcare, pharmaceuticals and other industries requiring the highest levels of security and privacy in customer communications.

The rapid growth of the Internet as a sales and service channel has brought the need for organizations to respond to large volumes of email from their customers and partners. This need to transmit financial information and other sensitive customer data over the Internet has made security a paramount concern for organizations aiming to increase the satisfaction and loyalty of their online customers. In addition, organizations are looking for ways to integrate email response and online customer service with other customer touch points, including call centers, field sales, reseller channels, retail and dealer networks.

"Customers and business partners have clearly expressed their preference for email interaction with corporations, but concerns over security have hampered the sending of sensitive information over the internet," said Matt Cain, vice president of Web and collaboration strategies at META Group. "The Siebel/Tumbleweed partnership underscores the requirement to make secure delivery of email over the internet an essential component of customer collaboration strategies."

Tumbleweed and Siebel Systems will address these requirements by integrating Tumbleweed secure Internet messaging technology with Siebel eBusiness Applications encompassing sales, marketing and service across all communication channels. Tumbleweed IME is a platform and set of applications for creating secure email channels between a business and its customers, partners, and suppliers. Siebel eMail Response, which works seamlessly with the Siebel eService suite of online customer service applications, is a complete email response management system that allows customer service agents to respond promptly and professionally to high volumes of incoming emails. The combination of Tumbleweed IME, Siebel eMail Response and Siebel eService provides organizations in such industries as retail banking and brokerage, institutional finance, and insurance with the industry's most comprehensive solution for secure, Internet-based customer communications.

"We believe that security is a critical element in successful online customer service," said David Schmaier, senior vice president of Products at Siebel Systems. "Enterprises who communicate with their customers via a secure online channel demonstrate the respect they have for customer data and for customer relationships. Tumbleweed Communications carries more secure messages online than any other company, and has developed significant expertise in building and deploying secure communications channels that enterprises use daily to reach out to customers. The integration of Tumbleweed IME with Siebel eBusiness Applications enables organizations of all sizes to measurably increase customer satisfaction, resulting in greater revenue and profitability."

"Siebel Systems has an extraordinary track record in eBusiness applications for customer response management, and we believe that Siebel eMail Response and Siebel eService represent the industry's best email response management and Web service applications," said Jeffrey C. Smith, president and CEO at Tumbleweed Communications. "Siebel Systems, the clear leader in customer-focused eBusiness solutions, has once again demonstrated market leadership by emphasizing the importance of security in online customer response management. We are delighted to partner with Siebel Systems to offer a compelling solution to address the mission-critical needs of our joint customers."

About Siebel Systems
Siebel Systems, Inc. (Nasdaq: SEBL) is the world's leading provider of applications software. Siebel Systems provides an integrated family of eBusiness applications software enabling multichannel sales, marketing and customer service systems to be deployed over the Web, call centers, field, reseller channels, retail and dealer networks. Siebel Systems' sales and service facilities are located in more than 28 countries. For more information, please visit Siebel Systems' Web site at www.siebel.com.

About Tumbleweed Communications Corp.
Tumbleweed is a leading provider of solutions for managing secure communication and collaboration to enable the business Internet. Tumbleweed's robust policy-based framework empowers organizations to safely share and protect critical information, increase customer loyalty and privacy and dramatically reduce costs. Tumbleweed is trusted by 1,000 blue-chip customers including American Express, Chevron, Datek Online, the European Union's Joint Research Council, First Union Wachovia, John Deere, Merrill Lynch, Nike, Northern Trust, NTT, Salomon Smith Barney, Travelers and US Food and Drug Administration. One hundred of the Fortune 500 are Tumbleweed customers. Tumbleweed Communications was founded in 1993 and is headquartered in Redwood City, Calif., with offices around the world.

Except for the historical information contained herein, the matters discussed in this press release may constitute forward-looking statements that involve risks and uncertainties that could cause actual results to differ materially from those projected, particularly with respect to the security features of Tumbleweed's products and the activities of any third party. In some cases, forward-looking statements can be identified by terminology such as "may," "will," "should," "potential," "continue," "expects," "anticipates," "intends," "plans," "believes," "estimates," and similar expressions. For further cautions about the risks of investing in Tumbleweed, we refer you to the documents Tumbleweed files from time to time with the Securities and Exchange Commission, particularly Tumbleweed's Form 10-K filed March 30, 2001 and Form 10-Q filed November 13, 2001. Tumbleweed assumes no obligation to update information contained in this press release.