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                                                                  EXHIBIT 2.2

                             STOCK OPTION AGREEMENT


            STOCK OPTION AGREEMENT (the "Agreement"), dated as of June 28,
2000, by and between Tumbleweed Communications Corp., a Delaware
corporation ("Parent"), and Interface Systems, Inc., a Michigan corporation
(the "Company").

                                   WITNESSETH:



            WHEREAS, concurrently with the execution and delivery of this
Agreement, the Company, Parent and Maize Acquisition Sub, Inc., a Delaware
corporation ("Sub"), are entering into an Agreement and Plan of Merger, dated as
of the date hereof (the "Merger Agreement"), which provides that, among other
things, upon the terms and subject to the conditions thereof, Sub will be merged
with and into the Company (the "Merger"), with the Company continuing as the
surviving corporation; and

            WHEREAS, as a condition and inducement to Parent's willingness to
enter into the Merger Agreement, Parent has required that the Company agree, and
the Company has so agreed, to grant to Parent an option with respect to certain
shares of the Company's authorized but unissued common stock on the terms and
subject to the conditions set forth herein.

            NOW, THEREFORE, to induce Parent and Sub to enter into the Merger
Agreement and in consideration of the representations, warranties, covenants and
agreements set forth herein and in the Merger Agreement, the parties hereto
intending to be legally bound, hereby agree as follows. Capitalized terms used
herein but not defined herein shall have the meanings set forth in the Merger
Agreement.

            1. GRANT OF OPTION. The Company hereby grants Parent an irrevocable
option (the "Option") to purchase a number of shares (the "Shares") of common
stock, no par value per share, of the Company (the "Company Common Stock"),
equal to the Option Number (as defined hereinafter), on the terms and subject to
the conditions set forth below.

            2.   EXERCISE OF OPTION.

                 (a) Exercise. At any time or from time to time prior to the
termination of the Option granted hereunder in accordance with the terms of this
Agreement, Parent (or its designee) may exercise the Option, in whole or in
part, if on or after the date hereof:

                     (i) any corporation, partnership, individual, trust,
unincorporated association, or other entity or "person" (as defined in Section
13(d)(3) of the Securities Exchange Act of 1934, as amended (the "Exchange
Act")) other than Parent or any of its "affiliates" (as defined in the Exchange
Act) (a "Third Party"), shall have:

                         (A) commenced or announced an intention to commence a
      bona fide tender offer or exchange offer for any shares of Company Common
      Stock, the consummation of which would result in "beneficial ownership"
      (as defined under Rule 13d-3 of the Exchange
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      Act) by such Third Party (together with all such Third Party's
      affiliates and "associates" (as such term is defined in the Exchange
      Act)) of 20% or more of the then voting equity of the Company (either
      on a primary or a fully diluted basis);

                         (B) filed a Notification and Report Form under the
      Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the "HSR
      Act"), reflecting an intent to acquire the Company or any assets or
      securities of the Company;

                         (C) solicited "proxies" in a "solicitation" subject to
      the proxy rules under the Exchange Act, executed any written consent or
      become a "participant" in any "solicitation" (as such terms are defined in
      Regulation 14A under the Exchange Act), in each case with respect to the
      Company Common Stock; or

                     (ii)     any of the events described in Section 7.2(b)
of the Merger Agreement that would require the Company to pay Parent the fee set
forth therein (but without the necessity of Parent having terminated the Merger
Agreement).

                     (iii)    Each of the events described in clauses (i) and
(ii) hereof shall be referred to herein as a "Trigger Event." The Company shall
notify Parent promptly in writing of the occurrence of any Trigger Event;
however, such notice shall not be a condition to the right of Parent to exercise
the Option.

                 (b) Exercise Procedure. In the event Parent wishes to exercise
the Option, Parent shall deliver to the Company a written notice (an "Exercise
Notice") specifying the total number of the Shares it wishes to purchase. To the
extent permitted by law and the Certificate of Incorporation of the Company and
provided that the conditions set forth in Section 3 hereof to Company's
obligation to issue the Shares to Parent hereunder have been satisfied or
waived, Parent shall, upon delivery of the Exercise Notice and tender of the
applicable aggregate Exercise Price, immediately be deemed to be the holder of
record of the shares of the Company Common Stock issuable upon such exercise,
notwithstanding that the stock transfer books of the Company shall then be
closed or that certificates representing such shares of the Company Common Stock
shall not heretofore have been delivered to Parent. Each closing of a purchase
of the Shares (a "Closing") shall occur at a place, on a date and at a time
designated by Parent in an Exercise Notice delivered at least two business days
prior to the date of the Closing.

                 (c) Termination of the Option. The Option shall terminate upon
the earlier of: (i) the Effective Time of the Merger; and (ii) the termination
of the Merger Agreement pursuant to Section 7.1(a), (b) or (c) thereof; and
(iii) twelve (12) months following the termination of the Merger Agreement
pursuant to Section 7.1(d) or (e) thereof. Notwithstanding the foregoing, if the
Option cannot be exercised by reason of any applicable judgment, decree, order,
law or regulation, the Option shall remain exercisable and shall not terminate
until the earlier of (x) the date on which such impediment shall become final
and not subject to appeal and (y) 5:00 p.m. Pacific Standard Time, on the tenth
(10th) business day after such impediment shall have been removed. The rights of
Parent set forth in Sections 7 and 8 shall not terminate upon termination of
Parent's

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right to exercise the Option, but shall extend to the time provided in
such sections. Notwithstanding the termination of the Option, Parent shall be
entitled to purchase the shares of the Company Common Stock with respect to
which Parent had exercised the Option prior to such termination.

                  (d) Option Number. The "Option Number" shall initially be the
number of shares equal to nineteen and nine-tenths percent (19.9%) of the total
number of shares of the Company Common Stock issued and outstanding as of the
date of this Agreement, and shall be adjusted hereafter to reflect changes in
the Company's capitalization occurring after the date hereof in accordance with
Section 11 hereof. Notwithstanding any other provision of this Agreement, in no
event shall the Option Number exceed nineteen and nine-tenths percent (19.9%) of
the total number of shares of the Company Common Stock issued and outstanding as
of the date of this Agreement, adjusted in accordance with Section 11 hereof.

                 (e) Exercise Price. The purchase price per share of the Company
Common Stock pursuant to the Option (the "Exercise Price") shall be $13.33.

            3. CONDITIONS TO CLOSING. The obligation of the Company to issue the
Shares to Parent hereunder is subject to the conditions that (i) all consents,
approvals, orders or authorizations of, or registrations, declarations or
filings with, any federal, state or local administrative agency or commission or
other federal state or local governmental authority or instrumentality, if any,
required in connection with the issuance of the Shares and the acquisition of
such shares by Parent hereunder shall have been obtained or made, as the case
may be; and (ii) no preliminary or permanent injunction or other order by any
court of competent jurisdiction prohibiting or otherwise restraining such
issuance shall be in effect.

            4.   CLOSING.  At any Closing,

                 (a) the Company shall deliver to Parent a single certificate in
definitive form representing the number of the Shares designated by Parent in
its Exercise Notice, such certificate to be registered in the name of Parent and
to bear the legend set forth in Section 11 hereof;

                 (b) Parent shall deliver to the Company the aggregate price for
the Shares so designated and being purchased by wire transfer of immediately
available funds to the account or accounts specified in writing by the Company;

                 (c) the Company shall pay all expenses, and any and all
federal, state and local taxes and other charges that may be payable in
connection with the preparation, issue and delivery of stock certificates under
this Section 4; and

                 (d) the Company shall cause the shares of the Company Common
Stock being delivered at the Closing to be approved for quotation on the Nasdaq
National Market and shall pay all expenses in connection with the application
for approval of such quotation. At any Closing at which Parent is exercising the
Option in part, Parent shall present and surrender this Agreement to the
Company, and the Company shall deliver to Parent an executed new agreement with
the same terms as this Agreement evincing the
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right to purchase the balance of the shares of the Company Common Stock
purchasable hereunder.

            5. REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company
represents and warrants to Parent that:

                 (a) the Company is a corporation duly organized, validly
existing and in good standing under the laws of the State of Michigan and has
the corporate power and authority to enter into this Agreement and to carry out
its obligations hereunder;

                 (b) the execution and delivery of this Agreement by the Company
and the consummation by the Company of the transactions contemplated hereby have
been duly authorized by all necessary corporate action on the part of the
Company and no other corporate proceedings on the part of the Company are
necessary to authorize this Agreement or any of the transactions contemplated
hereby;

                 (c) this Agreement has been duly executed and delivered by the
Company and constitutes a valid and binding obligation of the Company, and,
assuming this Agreement constitutes a valid and binding obligation of Parent, is
enforceable against the Company in accordance with its terms, except as
enforceability may be limited by bankruptcy and other laws affecting the rights
and remedies of creditors generally and general principles of equity;

                 (d) the Company has taken all necessary corporate action to
authorize and reserve for issuance and to permit it to issue, upon exercise of
the Option, and at all times from the date hereof through the expiration of the
Option will have reserved a number of authorized and unissued shares of the
Company Common Stock not less than the Option Number, such amount being subject
to adjustment as provided in Section 9 hereof, all of which, upon their issuance
and delivery in accordance with the terms of this Agreement, will be validly
issued, fully paid and nonassessable;

                 (e) upon delivery of the Shares to Parent upon the exercise of
the Option, Parent will acquire the Shares free and clear of all claims, liens,
charges, encumbrances and security interests of any nature whatsoever;

                 (f) the execution and delivery of this Agreement by the Company
does not, and the performance of this Agreement by the Company will not,
conflict with, or result in any violation of, or default (with or without notice
or lapse of time, or both) under, or give rise to a right of termination,
cancellation or acceleration of any obligation or the loss of a benefit under,
or the creation of a lien, pledge, security interest or other encumbrance on
assets pursuant to (any such conflict, violation, default, right of termination,
cancellation or acceleration, loss or creation, a "Violation"), (A) any
provision of the Articles of Incorporation, or Bylaws, of the Company or (B) any
provisions of any mortgage, indenture, lease, contract or other agreement,
instrument, permit, concession, franchise, or license or (C) any judgment,
order, decree, statute, law, ordinance, rule or regulation applicable to the
Company or its properties or assets, which Violation, in the case of each of
clauses (B) and (C), would have a material adverse effect on the Company;


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                 (g) except as contemplated by Section 8(b) hereof and as may be
required under the Securities Act of 1933, as amended (the "Securities Act"),
the execution and delivery of this Agreement by the Company does not, and the
performance of this Agreement by the Company will not, require any consent,
approval, authorization or permit of, or filing with or notification to, any
governmental or regulatory authority; and

                 (h) none of the Company or any of its affiliates or anyone
acting on its or their behalf has issued, sold or offered any security of the
Company to any person or entity under circumstances that would cause the
issuance and sale of shares of the Company Common Stock hereunder to be subject
to the registration requirements of the Securities Act as in effect on the date
hereof, and, assuming the representations and warranties of Parent contained in
Section 6(f) are true and correct, the issuance, sale and delivery of the shares
of the Company Common Stock hereunder would be exempt from the registration and
prospectus delivery requirements of the Securities Act, as in effect on the date
hereof, and the Company shall not take any action which would cause the
issuance, sale, and delivery of shares of the Company Common Stock hereunder not
to be exempt from such requirements.

            6. REPRESENTATIONS AND WARRANTIES OF PARENT. Parent represents
and warrants to the Company that:

                 (a) Parent is a corporation duly organized, validly existing
and in good standing under the laws of the State of Delaware and has the
corporate power and authority to enter into this Agreement and to carry out its
obligations hereunder;

                 (b) the execution and delivery of this Agreement by Parent and
the consummation by Parent of the transactions contemplated hereby have been
duly authorized by all necessary corporate action on the part of Parent and no
other corporate proceedings on the part of Parent are necessary to authorize
this Agreement or any of the transactions contemplated hereby;

                 (c) this Agreement has been duly executed and delivered by
Parent and constitutes a valid and binding obligation of Parent, and, assuming
this Agreement constitutes a valid and binding obligation of the Company, is
enforceable against Parent in accordance with its terms, except as
enforceability may be limited by bankruptcy and other laws affecting the rights
and remedies of creditors generally and general principles of equity;

                 (d) the execution and delivery of this Agreement by Parent does
not, and the performance of this Agreement by Parent will not, result in any
Violation pursuant to, (A) any provision of the Certificate of Incorporation or
By-laws of Parent, (B) any provisions of any mortgage, indenture, lease,
contract or other agreement, instrument, permit, concession, franchise, or
license or (C) any judgment, order, decree, statute, law, ordinance, rule or
regulation applicable to Parent or its properties or assets, which Violation, in
the case of each of clauses (B) and (C), would have a material adverse effect on
Parent;



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                 (e) except as contemplated by Section 8(b) hereof and as may be
required under the Securities Act, the execution and delivery of this Agreement
by Parent does not, and the performance of this Agreement by Parent will not,
require any consent, approval, authorization or permit of, or filing with or
notification to, any governmental or regulatory authority;

                 (f) any shares of the Company Common Stock acquired by Parent
upon exercise of the Option will be acquired for Parent's own account, for
investment purposes only and will not be, and the Option is not being, acquired
by Parent with a view to the public distribution thereof, in violation of any
applicable provision of the Securities Act.

            7.   CERTAIN REPURCHASES.

                 (a) Parent Put. At any time during which the Option is
exercisable pursuant to Section 2 hereof (the "Repurchase Period"), upon demand
by Parent, Parent shall have the right to sell to the Company (or any successor
entity thereof) and the Company (or such successor entity) shall be obligated to
repurchase from Parent (the "Put"), all or any portion of the Option, at the
price set forth in subparagraph (i) below, or all or any portion of the Shares
purchased by Parent pursuant to the exercise of the Option, at a price set forth
in subparagraph (ii) below:

                     (i) The difference between the "Market/Tender Offer Price"
for shares of the Company Common Stock as of the date (the "Notice Date") notice
of exercise of the Put, is given to the Company (defined as the higher of (A)
the price per share offered as of the Notice Date pursuant to any tender or
exchange offer or other Alternative Transaction (as defined in the Merger
Agreement) which was made prior to the Notice Date and not terminated or
withdrawn as of the Notice Date (the "Tender Price") and (B) the average of the
closing prices of shares of the Company Common Stock on the Nasdaq National
Market for the ten trading days immediately preceding the Notice Date, (the
"Market Price")), and the Exercise Price, multiplied by the number of the Shares
purchasable pursuant to the Option (or portion thereof with respect to which
Parent is exercising its rights under this Section 7), but only if the
Market/Tender Offer Price is greater than the Exercise Price. For purposes of
determining the highest price offered pursuant to any Alternative Transaction
which involves consideration other than cash, the value of such consideration
shall be equal to the higher of (x) if securities of the same class of the
proponent as such consideration are traded on any national securities exchange
or by any registered securities association, a value based on the closing sale
price or asked price for such securities on their principal trading market on
such date and (y) the value ascribed to such consideration by the proponent of
such Alternative Transaction, or if no such value is ascribed, a value
determined in reasonable good faith by the Board of Directors of the Company.

                     (ii)     The Exercise Price paid by Parent for the Shares
acquired pursuant to the exercise of the Option plus the difference between the
Market/Tender Offer Price and the Exercise Price, but only if the Market/Tender
Offer Price is greater than the Exercise Price, multiplied by the number of the
Shares so purchased.


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                     (iii)    For purposes of clauses (i) and (ii) of this
Section 7(a), the Tender Price shall be the highest price per share offered
pursuant to a tender or exchange offer or other Alternative Transaction during
the Repurchase Period.

                 (b) Payment and Redelivery of the Option or Shares. In the
event Parent exercises its rights under this Section 7, the Company shall,
within ten business days of the Notice Date, pay the required amount to Parent
in immediately available funds and Parent shall surrender to the Company the
Option or the certificates evidencing the Shares purchased by Parent pursuant
thereto, and Parent shall warrant that it owns such shares and that such shares
are then free and clear of all liens, claims, charges and encumbrances of any
kind or nature whatsoever.

            8.   REGISTRATION RIGHTS.

                 (a) Following the termination of the Merger Agreement and
exercise of the Option, Parent may by written notice request the Company to
register for resale under the Securities Act all or any part of the Shares
beneficially owned by Parent (the "Registrable Securities") in a firm commitment
offering. The Company shall use its reasonable best efforts to effect, as
promptly as practicable, the registration under the Securities Act of the
Registrable Securities; provided, however, that (i) Parent shall not be entitled
to demand more than an aggregate of two (2) effective registration statements
hereunder, and (ii) the Company will not be required to file any such
registration statement during any period of time (not to exceed sixty (60) days
after such request in the case of clause (A) below or ninety (90) days after
such request in the case of clauses (B) and (C) below) when (A) the Registrant
is in possession of material non-public information which it reasonably believes
would be detrimental to be disclosed at such time and, in the opinion of counsel
to the Company, such information would be required to be disclosed if a
registration statement were filed at that time; (B) the Company is required
under the Securities Act to include audited financial statements for any period
in such registration statement and such financial statements are not yet
available for inclusion in such registration statement; or (C) the Company
determines, in its reasonable judgment, that such registration would interfere
with any financing, acquisition or other transaction involving the Company or
any of its material subsidiaries and that such transaction is material to the
Registrant and its subsidiaries taken as a whole.

                 (b) The Company shall use its reasonable best efforts to cause
any Registrable Securities registered pursuant to this Section 8 to be qualified
for sale under the securities or Blue Sky laws of such jurisdictions as Parent
may reasonably request and shall continue such registration or qualification in
effect in such jurisdiction; provided, however, that the Company shall not be
required to qualify to do business in, or consent to general service of process
in, any jurisdiction by reason of this provision.

                 (c) The registration rights set forth in this Section 8 are
subject to the condition that Parent shall provide the Company with such
information with respect to its Registrable Securities, the plans for the
distribution thereof, and such other information with respect to the Parent as,
in the reasonable judgment of counsel for the Company, is necessary to enable
the Registrant to include in such registration statement all material facts
required to be disclosed with respect to a registration thereunder.

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                 (d) A registration effected under this Section 8 shall be
effected at the Company's expense, except for underwriting discounts and
commissions and the fees and the expenses of counsel to the Parent, and the
Registrant shall provide to the underwriters such documentation (including
certificates, opinions of counsel and "comfort" letters from auditors) as is
customary in connection with underwritten public offerings as such underwriters
may reasonably require.

                 (e) In connection with any registration effected under this
Section 8, the parties agree (i) to indemnify each other and the underwriters,
if any, in the customary manner, (ii) to enter into an underwriting agreement in
form and substance customary for transactions of such type with the underwriters
participating in such offering, if any, and (iii) to take all further actions
which shall be reasonably necessary to effect such registration and sale
(including if the managing underwriter deems it necessary, participating in
road-show presentations).

            9.   ADJUSTMENT UPON CHANGES IN CAPITALIZATION.

                 (a) In the event of any change in the Company Common Stock by
reason of stock dividends, splitups, mergers (other than the Merger),
recapitalizations, combinations, exchange of shares or the like, the type and
number of shares or securities subject to the Option, and the purchase price per
share provided in Section 2(e) hereof, shall be adjusted appropriately, and
proper provision shall be made in the agreements governing such transaction so
that Parent shall receive, upon exercise of the Option, the number and class of
shares or other securities or property that Parent would have received in
respect of the Company Common Stock if the Option had been exercised immediately
prior to such event or the record date therefor, as applicable.

                 (b) In the event that the Company shall enter in an agreement:
(i) to consolidate with or merge into any person, other than Parent or one of
its Subsidiaries, and shall not be the continuing or surviving corporation of
such consolidation or merger; (ii) to permit any person, other than Parent or
one of its Subsidiaries, to merge into the Company and the Company shall be the
continuing or surviving corporation, but, in connection with such merger, in the
then-outstanding shares of the Company Common Stock shall be changed into or
exchanged for stock or other securities of the Company or any other person or
cash or any other property or the outstanding shares of the Company Common Stock
immediately prior to such merger shall after such merger represent less than 50%
of the outstanding shares and share equivalents of the merged company; or (iii)
to sell or otherwise transfer all or substantially all of its assets to any
person, other than Parent or one of its Subsidiaries, then, and in each such
case, the agreement governing such transaction shall make proper provisions so
that upon the consummation of any such transaction and upon the terms and
conditions set forth herein, Parent shall receive for each the Share with
respect to which the Option has not been exercised an amount of consideration in
the form of and equal to the per share amount of consideration that would be
received by the holder of one share of the Company Common Stock less the
Exercise Price (and, in the event of an election or similar arrangement with
respect to the type of consideration to be received by the holders of the
Company Common Stock, subject to the foregoing, proper provision shall be made
so that the holder of the Option

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would have the same election or similar rights as would the holder of the number
of shares of the Company Common Stock for which the Option is then exercisable).

            10.  LIMITATION OF PARENT PROFIT.

                 (a) Notwithstanding any other provision of this Agreement, in
no event shall Parent's Total Profit (as defined below) exceed the aggregate
amount of fees and expenses payable under the provisions of Section 7.2(b) of
the Merger Agreement, and, if Parent's Total Profit shall otherwise exceed such
amount, Parent, at its sole election, shall either (i) reduce the number of
shares of Company Common Stock subject to this Option, (ii) deliver to the
Company for cancellation Shares previously purchased by Parent (valued, for
purposes of this Section 10(a) at the average closing sales price per share of
Company Common Stock (or if there is no sale on such date then the average
between the closing bid and ask prices on any such day) as quoted on the Nasdaq
National Market based on published financial sources for the twenty consecutive
trading days preceding the day on which Parent's Total Profit exceeds the
aggregate amount of fees and expenses payable under the provisions of Section
7.2(b) of the Merger Agreement, (iii) pay cash to the Company, or (iv) any
combination thereof, such that Parent's actually realized Total Profit shall not
exceed the aggregate amount of fees and expenses payable under the provisions of
Section 7.2(b) of the Merger Agreement after taking into account the foregoing
actions.

                 (b) As used herein, the term "Total Profit" shall mean the
amount (before taxes) of the following: (a) the aggregate amount of (i)(x) the
net cash amounts received by Parent or its permitted designees or any affiliated
party pursuant to the sale of Shares (or any other securities into which the
Option is converted or exchanged) to any unaffiliated party or to the Company
pursuant to this Agreement, less (y) Parent's or its permitted designees
purchase price of such Shares, (ii) any amounts received by Parent or its
permitted designees or any affiliated party on the transfer of the Option (or
any portion thereof) to any unaffiliated party or to the Company pursuant to
this Agreement, and (iii) any amounts received by Parent pursuant to Section
7.2(b) of the Merger Agreement; minus (b) the amount of cash theretofore paid to
the Company pursuant to this Section 10 plus the value of the Shares theretofore
delivered to the Company for cancellation pursuant to this Section 10.

            11.  RESTRICTIVE LEGENDS.  Each certificate representing
shares of the Company Common Stock issued to Parent hereunder shall include a
legend in substantially the following form:

            THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY BE REOFFERED OR
SOLD ONLY IF SO REGISTERED OR IF AN EXEMPTION FROM SUCH REGISTRATION IS
AVAILABLE.

            It is understood and agreed that (i) the reference to the resale
restrictions of the Securities Act and state securities or Blue Sky laws in the
foregoing legend shall be removed by delivery of substitute certificate(s)
without such reference if Parent shall have delivered to the Company a copy of a
letter from the staff of the Securities and Exchange Commission, or an opinion
of counsel, in form and substance reasonably

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satisfactory to the Company, to the effect that such legend is not required for
purposes of the Securities Act or such laws; (ii) the reference to the
provisions of this Agreement in the foregoing legend shall be removed by
delivery of substitute certificate(s) without such reference if the shares have
been sold or transferred in compliance with the provisions of this Agreement and
under circumstances that do not require the retention of such reference; and
(iii) the legend shall be removed in its entirety if the conditions in the
preceding clauses (i) and (ii) are both satisfied. In addition, such
certificates shall bear any other legend as may be required by law. Certificates
representing shares sold in a registered public offering pursuant to Section 8
shall not be required to bear the legend set forth in this Section 11.

            12. BINDING EFFECT; NO ASSIGNMENT. This Agreement shall be binding
upon and inure to the benefit of the parties hereto and their respective
successors and permitted assigns. Except as expressly provided for in this
Agreement, neither this Agreement nor the rights or the obligations of either
party hereto are assignable, except by operation of law, or with the written
consent of the other party. Nothing contained in this Agreement, express or
implied, is intended to confer upon any person other than the parties hereto and
their respective permitted assigns any rights or remedies of any nature
whatsoever by reason of this Agreement.

            13. SPECIFIC PERFORMANCE. The parties recognize and agree that if
for any reason any of the provisions of this Agreement are not performed in
accordance with their specific terms or are otherwise breached, immediate and
irreparable harm or injury would be caused for which money damages would not be
an adequate remedy. Accordingly, each party agrees that, in addition to other
remedies, the other party shall be entitled to an injunction restraining any
violation or threatened violation of the provisions of this Agreement. In the
event that any action should be brought in equity to enforce the provisions of
this Agreement, neither party will allege, and each party hereby waives the
defense, that there is adequate remedy at law.

            14. ENTIRE AGREEMENT. This Agreement, the Merger Agreement, the
other Ancillary Agreements and the Confidentiality Agreement constitute the
entire agreement among the parties with respect to the subject matter hereof and
supersede all other prior agreements and understandings, both written and oral,
among the parties or any of them with respect to the subject matter hereof.

            15. FURTHER ASSURANCE. Each party will execute and deliver all
such further documents and instruments and take all such further action as
may be necessary in order to consummate the transactions contemplated
hereby.

            16. VALIDITY. The invalidity or unenforceability of any provision of
this Agreement shall not affect the validity or enforceability of the other
provisions of this Agreement, which shall remain in full force and effect. In
the event any court or other competent authority holds any provision of this
Agreement to be null, void or unenforceable, the parties hereto shall negotiate
in good faith the execution and delivery of an amendment to this Agreement in
order, as nearly as possible, to effectuate, to the extent permitted by law, the
intent of the parties hereto with respect to such provision. Each party agrees
that, should any court or

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other competent authority hold any provision of this Agreement or part hereof to
be null, void or unenforceable, or order any party to take any action
inconsistent herewith, or not take any action required herein, the other party
shall not be entitled to specific performance of such provision or part hereof
or to any other remedy, including but not limited to money damages, for breach
hereof or of any other provision of this Agreement or part hereof as the result
of such holding or order.

            17. NOTICES. Any notice or communication required or permitted
hereunder shall be in writing and either delivered personally, telegraphed or
telecopied or sent by certified or registered mail, postage prepaid, and shall
be deemed to be given, dated and received when so delivered personally,
telegraphed or telecopied or, if mailed, five business days after the date of
mailing to the following address or facsimile number, or to such other address
or addresses as such person may subsequently designate by notice given
hereunder.

                     (i) if to Parent, to:

                 Tumbleweed Communications Corp.
                 700 Saginaw Drive
                 Redwood City, California  94063
                 Attention:   Jeffrey C. Smith
                 Telephone:   650-216-2010
                 Facsimile:   650-216-2001

                 with a copy to:

                 Skadden, Arps, Slate, Meagher & Flom LLP
                 525 University Avenue
                 Palo Alto, CA  94301
                 Attention:  Gregory C. Smith
                 Telephone No:    650-470-4500
                 Facsimile No.:  650-470-4570

                     (ii)     if to the Company, to:

                 Interface Systems, Inc.
                 5855 Interface Drive
                 Ann Arbor, Michigan  48103
                 Attention:   Robert A. Nero
                 Telephone:   734-769-5900
                 Facsimile:   734-769-1047


                 with a copy to:

                 Dykema Gossett PLLC
                 400 Renaissance Center
                 Detroit, Michigan 48243
                 Attention:   Aleksandra A. Miziolek
                 Telephone No.:  313-568-6762
                 Facsimile No.:   313-568-6915


   12
            18. GOVERNING LAW. This Agreement shall be governed by and construed
in accordance with the laws of the State of Delaware, without giving effect to
the principles of conflicts of law thereof.

            19. DESCRIPTIVE HEADINGS. The descriptive headings herein are
inserted for convenience of reference only and are not intended to be part
of or to affect the meaning or interpretation of this Agreement.

            20. COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original, but all of
which, taken together, shall constitute one and the same instrument.

            21. EXPENSES. Except as otherwise expressly provided herein or
in the Merger Agreement, all costs and expenses incurred in connection with
the transactions contemplated by this Agreement shall be paid by the party
incurring such expenses.

            22. AMENDMENTS; WAIVER. This Agreement may be amended by the parties
hereto and the terms and conditions hereof may be waived only by an instrument
in writing signed on behalf of each of the parties hereto, or, in the case of a
waiver, by an instrument signed on behalf of the party waiving compliance.

            IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed by their respective duly authorized officers as of the date first
above written.


                                     INTERFACE SYSTEMS, INC.


                                     By:
                                        --------------------------
                                        Name:
                                        Title:


                                    TUMBLEWEED COMMUNICATIONS CORP


                                     By:
                                        --------------------------
                                        Name:
                                        Title: