CONCENTRIC NETWORK AND STAMPS.COM FORM STRATEGIC RELATIONSHIP TO BRING INTERNET POSTAGE TO SMALL AND MEDIUM-SIZED BUSINESSES

SAN JOSE, Calif., July 28, 1999 – Concentric Network Corp. (Nasdaq: CNCX), a leading provider of Internet solutions for small- and medium-sized businesses, today announced a strategic relationship with Stamps.com (Nasdaq: STMP), the innovator of Internet Postage, enabling users to print postage from their PCs. The agreement calls for Concentric to offer Stamps.com’s Internet Postage service to its business customers via its small business portal and various direct sales methods. The two companies will also participate in future co-marketing programs.

“With its large and growing base of small and mid-sized business customers, Concentric is an ideal partner to expand the reach of the Stamps.com service,” said John Payne, president and CEO of Stamps.com. “We are convinced that Concentric’s customers will find the service an easy, convenient and cost effective way to manage their postage needs, directly from their desktops. We’re very pleased to be helping Concentric show their business customers how going online can save time and money.”

Concentric customers will have the ability to print postage onto envelopes and labels using ordinary laser and inkjet printers 24 hours a day, seven days a week. The Internet Postage service developed by Stamps.com requires no set-up fees or additional hardware and has been approved by the U.S. Postal Service (USPS) for the final phase of Beta and market testing before commercial release. The promotional activities between Concentric and Stamps.com will begin upon USPS approval.

“Stamps.com is revolutionizing the way small businesses handle their postage needs and we’re extremely pleased to partner with them to offer our customers this cutting-edge service,” said Henry R. Nothhaft, chairman, president and CEO of Concentric Network. “This is another value-added offering in our portfolio of services aimed at the small business marketplace, and we anticipate great demand from our customers for the Stamps.com service.”

About Stamps.com

Stamps.com (NASDAQ: STMP) is a leading provider of highly secure transaction-oriented Internet services for small business, consumer and corporate users. Stamps.com partners include America Online, Inc. (AOL), Avery Dennison, Concentric Network Corporation, Office Depot, Intuit’s Quicken.com, Intel Corporation, MySoftware, Peachtree Software, Westvaco, and other leading Internet, office supply and technology companies.

Stamps.com is located at 3420 Ocean Park Blvd. Suite 1040, Santa Monica, CA 90405, tel (310) 581-7200, fax (310) 581-7500 and at http://sdcmainprod.wpengine.com.

About Concentric Network Corporation

Concentric Network Corporation provides complete, easy-to-use Internet business solutions for small- to medium-sized companies and customized Virtual Private Network and data center services for larger organizations. Concentric’s portfolio of services for small- to medium-sized companies includes high-speed DSL access, Web hosting and e-commerce. For larger organizations, the company offers dedicated Web hosting services and VPN solutions that enable an organization to securely and reliably communicate with its offices, mobile sales force, business partners, vendors and customers. Concentric’s services rely on a high-performance, ATM-based network that covers North America, and through various partnerships, reaches internationally. Concentric also operates state-of-the-art hosting centers at strategic locations across the U.S. All Concentric services are backed by 24 hour/7 days a week customer support, and many are backed by strong service level agreements.

The company recently received two Well-Connected Awards from Network Computing for Most Innovative Service Provider of the Year and for Best Enterprise Internet Service Provider for ConcentricHost(TM). The company consistently receives top ratings by Inverse Network Technology (www.inversenet.com), an independent research firm that grades the performance of network service providers each month. Traded on NASDAQ under the symbol “CNCX,” Concentric Network is headquartered in San Jose, Calif., with operations offices in Southern California, Chicago, Il., St. Louis, Mo., and Saginaw, Mich., along with sales and channel support across the U.S. For more information, access the company’s Web site at http://www.concentric.net or contact [email protected].

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Concentric Network Corporation and the Concentric logo are registered trademarks. All other trademarks are the property of their respective owners.

“Safe Harbor” Statement under the Private Securities Litigation Reform Act of 1995: This release may contain forward-looking statements that involve risks and uncertainties. Important factors which could cause actual results to differ materially from those in the forward-looking statements are detailed in filings with the Securities and Exchange Commission made from time to time by Stamps.com, Stamps.com’s prospectus related to its initial public offering that was filed with the SEC on June 25, 1999.