Filed by Interface Systems, Inc.
                                               Pursuant to Rule 425 under the
                                            Securities Act of 1933 and deemed
                                         filed pursuant to Rule 14a-12 of the
                                              Securities Exchange Act of 1934

                                                             Subject Company:
                                                      Interface Systems, Inc.
                                                Commission File No. 333-41692

Dear Shareholders:

On June 29th we announced that Interface reached an agreement with Tumbleweed
Communications Corp. (Nasdaq - TMWD) under which Interface would become a
wholly-owned subsidiary of Tumbleweed. Your board of directors has
unanimously voted to approve the merger based on our belief that the merger
is in the best interests of Interface shareholders. You will soon be
receiving a proxy statement/prospectus detailing the proposed transaction and
will be asked to vote on the merger. The affirmative vote of the holders of
a majority of the issued and outstanding shares of our stock is required to
complete the merger. YOUR VOTE IS VERY IMPORTANT. Your abstention or failure
to vote or failure to instruct your broker or nominee as to how to vote
shares that you own but that are not held in your name, will have the effect
of a vote against the merger.

Your board of directors recommends the merger primarily because it believes
that the merger will result in a combined company that has a significantly
greater opportunity than Interface does alone to play a leadership role in
the large and growing market for electronic statement presentment (ESP).
Tumbleweed and Interface combined would have greater financial,
technological, sales, marketing and human resources with which to pursue that
opportunity. As a result of the merger, our shareholders will be able to
participate in the long-term growth of a combined company which would have
the capability of providing current and future customers with a more complete
and comprehensive ESP solution.

As a leading provider of advanced messaging solutions for business
communications, Tumbleweed is well positioned to accelerate fulfillment of
many of the key elements of Interface's strategic plan - a more comprehensive
ESP solution, expansion into new vertical markets, greater presence in the
brokerage market, worldwide sales and marketing initiatives, divestiture of
non-Internet-related businesses and transition to a recurring revenue model -
that would otherwise have taken a year or longer to achieve.

In addition to the premium (approximately 41.3% over the average of the
closing market prices of Interface's common stock for thirty days prior to
the signing of the merger agreement) to be received by our shareholders,
there are many other reasons why we believe that the merger is in your best
interests. We urge you to read the proxy statement/prospectus (especially the
Section entitled "The Merger - Reasons for Interface Engaging in the Merger;
Recommendation of the Interface Board") which outlines these reasons and
provides you with additional information about important aspects of the
merger. Please remember to VOTE and return your proxy card as soon as you
receive it.



In the meantime, please feel free to e-mail your questions or comments to us
at nero@intface.com.

Sincerely,




Robert A. Nero
President and Chief Executive Officer

Garnel F. Graber
Chairman of the Board
- ------------------------------------------------------------------------------

Tumbleweed has filed a Registration Statement on Form S-4 with the Securities
and Exchange Commission (the "SEC") in connection with the merger and
Tumbleweed and Interface expect to mail a proxy statement/prospectus to
Interface shareholders containing information about the merger on or about
August 4, 2000. WE URGE INVESTORS AND SECURITY HOLDERS TO READ THE
REGISTRATION STATEMENT AND THE PROXY STATEMENT/PROSPECTUS CAREFULLY WHEN THEY
BECOME AVAILABLE. THE REGISTRATION STATEMENT AND THE PROXY
STATEMENT/PROSPECTUS WILL CONTAIN IMPORTANT INFORMATION ABOUT TUMBLEWEED,
INTERFACE, THE MERGER AND RELATED MATTERS. Investors and security holders
will be able to obtain these documents free of charge at the SEC's Web site,
http://www.sec.gov. In addition, both Tumbleweed and Interface file annual,
quarterly and special reports, proxy statements and other information with
the SEC. You may read and copy any reports, statements and other information
filed by Tumbleweed and Interface at the SEC's public reference rooms at
Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C. 20549 or at the
SEC's other public reference rooms in New York, New York and Chicago,
Illinois. Please call the SEC at 1-800-SEC-0330 for further information on
public reference rooms. Tumbleweed or Interface will provide, without charge,
a copy of any or all of their documents incorporated by reference in the
proxy statement/prospectus (other than exhibits to such documents, unless the
exhibits are specifically incorporated by reference in such documents.

In connection with the proposed merger, Interface will solicit proxies from
its shareholders to approve and adopt the merger agreement. Interface and the
following persons named below may be deemed to be "participants" in such
solicitation: the directors of Interface, Robert A. Nero (President and Chief
Executive Officer), Garnel F. Graber (Chairman of the Board), Bruce E.
Rhoades, David C. Seigle, Lloyd A. Semple and Thomas L. Thomas; and the
following executive officer and employee of Interface: Brian D. Brooks (Chief
Financial Officer). Information concerning such participants is set forth in
the registration statement filed with the SEC by Tumbleweed on August 3,
2000. The business address of each such participant is c/o Interface Systems,
Inc., 5855 Interface Drive, Ann Arbor, Michigan 48103.

PLEASE READ THE PROXY STATEMENT/PROSPECTUS CAREFULLY BEFORE MAKING A DECISION
CONCERNING THE MERGER. A description of any interests that Interface's
directors and executive officers have in the merger will be available in the
proxy statement/prospectus. Updated information with respect to the security
holdings of these individuals will be included in the final proxy
statement/prospectus to be filed with the SEC.

- -  CAUTIONARY STATEMENT - This document, the documents of Tumbleweed and
   Interface referenced herein and other communications to shareholders of
   Interface may contain "forward-looking statements" within the meaning of
   the Private Securities Litigation Reform Act of 1995. These statements
   included relate to expectations concerning matters that are not historical
   facts. Also, when Tumbleweed or Interface uses words such as "believes,"
   "expects," "anticipates" or similar expressions, we are making
   forward-looking statements. Although each of Tumbleweed and Interface
   believes that the expectations reflected in such



   forward-looking statements are reasonable, neither can give any assurance
   that such expectations will prove to have been correct. Important factors
   that could cause actual results to differ materially from such
   expectations are disclosed in the Registration Statement and the proxy
   statement/prospectus including but, without limitation, in the "Risk
   Factors" section of the proxy statement/prospectus.