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                                                                    Exhibit 99.1


PRESS RELEASE

TUMBLEWEED COMMUNICATIONS CORP. ANNOUNCES COMPLETION OF ACQUISITION OF INTERFACE
SYSTEMS, INC.

REDWOOD CITY, CA AND ANN ARBOR, MI --- SEPTEMBER 1, 2000---Tumbleweed
Communications Corp., a leading provider of Internet infrastructure for business
messaging, (NASDAQ:TMWD) and Interface Systems, Inc., a leading provider of
Legacy-to-Internet (L2i) technology, (NASDAQ:INTF) today jointly announced that
Tumbleweed completed its acquisition of Interface on September 1, 2000. Under
the terms of the merger agreement, each share of Interface common stock has been
converted into the right to receive 0.264 of a share of Tumbleweed common stock.
Letters of transmittal regarding the procedures to exchange Interface common
stock for Tumbleweed common stock will be sent to former Interface shareholders
in the near future. As a result of the acquisition, Interface shares will no
longer be listed on the NASDAQ stock market's national market.

Interface's industry-leading L2i-TM- suite of legacy data conversion products
and services and Tumbleweed's secure channel for electronic statement
presentment provide the necessary technologies and services to transform
electronic statement delivery and hasten its adoption.

"Tumbleweed IME and Interface's L2i products and services are a powerful
combination. Tumbleweed customers now benefit from a comprehensive end-to-end
solution for electronic statement presentment: legacy data conversion,
personalization, secure e-mail delivery, archival and an automated
inquiry/response loop," said Jeffrey C. Smith, President and CEO, Tumbleweed
Communications Corp. "Statement presentment is a significant market opportunity
for Tumbleweed. Interface's L2i technology will deepen our existing leadership
in this critical market."

"Electronic Bill Payment and Presentment (EBPP) vendors have focused on payment
rather presentment," continued Smith. "End users want to aggregate statements in
their existing e-mail boxes - and businesses want the same thing. They want to
build a valuable communications channel by presenting those statements to their
customers. Secure e-mail makes this possible. Legacy data conversion
automatically extracts the information critical to statements and prepares it to
be sent online, which speeds deployment of electronic statement presentment
systems. Tumbleweed's primary business goal is to increase the amount of traffic
that flows over our secure communications channel. Interface's legacy data
conversion services can drive
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substantive additional traffic over Tumbleweed IME."

Interface's industry-leading L2i products and services greatly simplify the
process of transforming and using data found in legacy systems into
electronic content that is easy to distribute and use online. The L2i
products can automatically take information from mainframe print streams and
intelligently convert it into formats such as pdf, HTML or XML for use
online. Tumbleweed's solutions enable the secure exchange of this information
between businesses and users via Tumbleweed Integrated Messaging Exchange-TM-
(IME-TM-), a platform and set of applications for creating secure
communication channels between a business and its customers, partners and
suppliers.

ABOUT TUMBLEWEED COMMUNICATIONS CORP.

Tumbleweed Communications Corp. is a leading provider of advanced e-mail
solutions for business communications. Our products and services enable
businesses to create and manage secure online communication channels that
leverage established e-mail networks and enterprise applications. Tumbleweed
Integrated Messaging Exchange is a platform and set of applications for creating
secure communications channels between a business and its customers, partners,
and suppliers. Tumbleweed Messaging Management System is a comprehensive
solution that extends internal e-mail systems to the Internet through
centralized security, policy enforcement, filtering and archiving. Used
together, Tumbleweed IME and Tumbleweed MMS automatically apply security
policies and redirect sensitive e-mail for secure, trackable delivery.

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 potential growth of Tumbleweed
and its subsidiaries. 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 S-1 filed July 26, 2000, Form S-4 filed August 3, 2000, Form
10-K filed March 30, 2000, and Form 10-Q filed August 14, 2000. Tumbleweed
assumes no obligation to update information contained in this press release.

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Tumbleweed is a registered trademark and Integrated Messaging Exchange, IME, and
Messaging Management System (MMS) are trademarks of Tumbleweed Communications
Corp.



FOR MORE INFORMATION:


For Press:

Lisa Poulson
Tumbleweed Communications
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650-216-2020
lisa.poulson@tumbleweed.com


For Investors:

Jennifer Ruddock
Tumbleweed Communications
650-216-2129
jennifer.ruddock@tumbleweed.com