Automated Anti-Spam Update Stops 15,000 Spam Emails Per Day

Redwood City, CA – September 8, 2004 – Tumbleweed® Communications Corp. (NASDAQ:TMWD), a leading provider of secure Internet messaging software and appliances for enterprises and government agencies, announced today that international law firm Cleary, Gottlieb, Steen & Hamilton has deployed Tumbleweed’s Dynamic Anti-Spam Service (DAS) to extend its existing email firewall implementation, resulting in a 99% spam capture rate with very few false positives.

“We were very impressed with the amount of spam captured by Tumbleweed’s email firewall and Dynamic Anti-Spam Service - with virtually no false positives,” said John Daggan, Cleary Gottlieb’s Network Manager. “End users were extremely pleased with the dramatic reduction in the amount of spam.”

Cleary Gottlieb, with more than 2,200 employees located in 12 offices worldwide, receives over 150,000 email messages each week. As the volume of spam has continued to rise and viruses and worm attacks have spread across the Internet, Cleary Gottlieb realized that a manual, signature-based approach to fighting spam would not be sufficient to keep pace with the ingenuity of spammers.

Cleary Gottlieb learned about Tumbleweed’s DAS and quickly implemented the automated spam update service. By capturing spam at the network perimeter, the firm saw an immediate 100% increase in its spam capture rate without adding additional management overhead, points of failure or significant cost. Cleary Gottlieb is now blocking more than 15,000 spam messages per day with almost no false positives, or legitimate messages being incorrectly identified as spam.

“Firms face an uphill battle against spam as spam tactics and threats rapidly evolve," said Tumbleweed’s Vice President of Marketing Jeff Ready. “The combination of Tumbleweed’s email firewall and DAS provides firms like Cleary Gottlieb with the necessary arsenal to protect their time, employees and resources from external email threats.”

About Tumbleweed's Email Firewall
Tumbleweed’s email firewall has been recognized as the #1 enterprise software solution for fighting spam, according to Network World (http://www.nwfusion.com/reviews/2003/0915spam.html), and the #1 email firewall software for large enterprises by Information Security magazine. Tumbleweed’s email firewall protects, filters and secures email traffic at the Internet gateway with an integrated set of anti-spam, anti-virus, anti-hacker, content filtering, email relay and encrypted messaging capabilities -- minimizing email communications risks and reducing email management costs. Tumbleweed’s email firewall is used by more than 400 of the world’s largest, most demanding messaging infrastructures, and is available in both appliance and software editions.

About Tumbleweed's Dynamic Anti-Spam Service
The Tumbleweed Dynamic Anti-Spam Service (DAS) is rated as the top anti-spam software and appliance for large enterprises by Network World magazine, and the product is currently used to block more than 32 million spam messages per day on behalf of our customers. DAS is an Internet-based subscription service that updates Tumbleweed’s e-mail firewall with new heuristic defenses as they are published, similar to the way anti-virus engines work. The email firewall includes a highly effective Spam Analysis Engine, which automates the identification of spam using powerful heuristics-based analysis technology; typical customers see an immediate 90%+ capture rate with one-tenth of one percent false positive rate before tuning. Tumbleweed's Message Protection Lab develops and publishes the heuristic updates: the lab is staffed by experts who continually analyze spam to identify new spammer trends and tactics, and create and publish new heuristics to stop them. The lab analyzes both spam and legitimate e-mail gathered internationally and provided by enterprise customers to ensure that the Dynamic Anti-Spam Service minimizes false positives in a business environment.

About Cleary Gottlieb
Founded in 1946 by lawyers committed to internationalism, diversity and excellence, Cleary Gottlieb is a leading international law firm that employs more than 800 lawyers around the world. Last year, Cleary Gottlieb received Chambers and Partners “Competition/Antitrust International Law Firm of the Year” award, and the firm ranked #1 in European M&A among U.S.-based firms. The firm has offices in New York, Washington, D.C., Paris, Brussels, London, Frankfurt, Cologne, Rome, Milan, Moscow, Hong Kong and Tokyo.

About Tumbleweed Communications Corp.
Tumbleweed is a leading provider of secure Internet messaging software and hardware for enterprises and government agencies. By making Internet communications secure, reliable and automated, Tumbleweed's anti-spam email firewall, secure file transfer, secure email, and identity validation solutions help customers significantly reduce the cost of doing business. Tumbleweed products are used to communicate with millions of end-users and tens of thousands of corporations. Tumbleweed has more than 600 enterprise customers, including ABN Amro, Bank of America Securities, Catholic Healthcare West, JP Morgan Chase & Co. The Regence Group (Blue Cross/Blue Shield), St. Luke's Episcopal Healthcare System, the US Food and Drug Administration, and the US Navy and Marine Corps. Tumbleweed Communications was founded in 1993 and is headquartered in Redwood City, California. For additional information about Tumbleweed go to www.tumbleweed.com or call 650-216-2000.

SAFE HARBOR STATEMENT
Tumbleweed cautions that forward-looking statements contained in this press release are based on current plans and expectations, and that a number of factors could cause the actual results to differ materially from the guidance given at this time. These factors are described in the Safe Harbor statement below.

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 features and performance of Tumbleweed’s Email Firewall and Dynamic Anti-Spam solutions. 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 15, 2004, Form 10-Q filed May 10, 2004, and Form 10-Q filed August 12, 2004.

Tumbleweed assumes no obligation to update information contained in this press release, including for example its guidance regarding its future performance, which represents the Company's expectations only as of the date of this release and should not be viewed as a statement about the Company's expectations after such date. Although this release may remain available on the Company's website or elsewhere, its continued availability does not indicate that the Company is reaffirming or confirming any of the information contained herein.