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                                                           EXHIBIT 10.4

                                    GUARANTY

         This GUARANTY (this "Guaranty") dated as of July 26, 2000, from HENRY
M. ZACHS, c/o ZIPLINK, INC., 40 Woodland Street, Hartford, Connecticut 06105
(the "Guarantor"), in favor of FLEET NATIONAL BANK, a national banking
association, with an office at 777 Main Street, Hartford, Connecticut 06115 (the
"Lender").

                                   WITNESSETH:

         WHEREAS, ZIPLINK, INC. (the "Borrower") has requested that the Lender
make a revolving credit loan to the Borrower in the maximum principal amount of
$10,000,000 (the "Loan"); and

         WHEREAS, it is a condition to Lender's making the Loan to the Borrower
that the Guarantor execute and deliver this Guaranty to the Lender; and

         WHEREAS, contemporaneously herewith the Lender and the Borrower are
entering into a Revolving Loan and Security Agreement of even date herewith (the
"Loan Agreement") pursuant to which the Lender will make the Loan; and

         WHEREAS, the Loan will be evidenced by the Borrower's Revolving Loan
Note of even date herewith (the "Note"); and

         WHEREAS, the obligations of Guarantor under this Guaranty are to be
secured by a Stock Pledge Agreement (the "Pledge Agreement") of even date
herewith, pursuant to which Guarantor has pledged certain Securities to the
Lender, and an Account Control Agreement to which the pledged Securities have
been subjected the ("Control Agreement); and

         WHEREAS, the Guarantor will receive material benefit from the Loan; and

         WHEREAS, capitalized terms not otherwise defined herein shall have the
meanings set forth in the Loan Agreement.

         NOW, THEREFORE, in consideration of the premises set forth above and
other good and valuable consideration, the receipt and adequacy of which are
hereby acknowledged, the parties hereto agree as follows:

         SECTION 1.     GUARANTY. The Guarantor does hereby unconditionally
guarantee to Lender the full and prompt payment and performance by the Borrower
of all of the obligations of every kind and nature whatsoever to be paid and
performed by the Borrower as and when required under the Loan Agreement, the
Note and the other Financing Documents, including, without limiting the
generality of the foregoing, the payment of all principal, interest and other

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sums under the Note (including, without limitation, any payment made by the
Borrower and required to be repaid to the Borrower or any other corporation,
natural person, firm, joint venture, partnership, trust, unincorporated
organization, limited liability Borrower, other form of business organization,
government, or department or agency of any government (any of the foregoing a
"Person") pursuant to any law relating to bankruptcy or insolvency by a court of
competent jurisdiction adjudicating the bankruptcy or insolvency of the
Borrower) and including the payment of all principal, interest, and other
sums under any and all Interest Rate Protection Contracts executed in connection
with the Loan Agreement (all of such obligations, as so described, being
referred to herein as the "Obligations"), in all respects strictly in accordance
with the terms of the Financing Documents. In the event of a default in
performance of any Obligation by the Borrower, the Guarantor shall promptly
perform or cause to be performed such Obligation upon receipt of written notice
of such default from Lender.

         SECTION 2.     CONSENTS AND WAIVERS BY GUARANTOR.

              (a)       This Guaranty shall be binding upon the Guarantor, his
heirs, successors and assigns, and shall remain in full force and effect
irrespective of, and shall not be terminated by, the existence of any law,
regulation or order now or hereafter in effect in any jurisdiction affecting the
terms of this Guaranty. The liability of the Guarantor under this Guaranty shall
be absolute, unconditional and irrevocable irrespective of:

                        (i)       any lack of validity or enforceability of the
Borrower's obligations under or with respect to the Loan Agreement, the Note or
any of the other Financing Documents or any other agreement or instrument
relating thereto;

                        (ii)      any change, pursuant to the terms of the Loan
Agreement, the Note or any of the other Financing Documents, whether or not
agreed to by the Guarantor, in the time, manner or place of performance of any
Obligation under, or in any other term of, the Loan Agreement, the Note or any
of the other Financing Documents or any other amendment, renewal, extension,
acceleration, compromise or waiver of or any consent or departure from the terms
or provisions of the Loan Agreement, the Note or any of the other Financing
Documents;

                        (iii)     the lack of power or authority of the Borrower
to execute and deliver the Loan Agreement, the Note or any of the other
Financing Documents or any other agreement or instrument relating thereto; any
defense, set-off or counterclaim which may at any time be available to or
asserted by the Borrower against Lender or any other Person except for the
defenses available to the Borrower based on the acts or omissions of the Lender;
the existence or continuance of the Borrower or any affiliate of the Borrower as
a legal entity; the consolidation or merger of the Borrower or any affiliate of
the Borrower with or into any other Person, or the sale, lease or other
disposition by the Borrower or any affiliate of the Borrower of all or
substantially all of its assets to any other Person, whether or not effected in
compliance with the provisions of the Financing Documents; or the bankruptcy or
insolvency of the Borrower or any affiliate of the Borrower, the admission in
writing by the Borrower or


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any affiliate of the Borrower of its inability to pay its debts as they mature,
or its making of a general assignment for the benefit of, or entering into a
composition or arrangement with, creditors; or

                        (iv)      any act, failure to act, delay or omission
whatsoever on the part of Lender, any failure to give to the Borrower or the
Guarantor notice of default in the making of any payment due and payable under
this Guaranty or the Loan Agreement, the Note or any of the other Financing
Documents or notice of any failure on the part of the Borrower to do any act or
thing or to observe or perform any covenant, condition or agreement by it to be
observed or performed under the Loan Agreement, the Note or any of the other
Financing Documents; or any action taken by Lender in the exercise of any right
or power or the failure, delay or omission to exercise any such right or power;
it being the purpose and intent of this Guaranty that the obligations of the
Guarantor hereunder shall be absolute, unconditional and irrevocable and shall
not be discharged or terminated except by full and complete payment and
performance of all of the Obligations.

              (b)       The Guarantor does hereby waive and relinquish, so far
as he may lawfully and effectively do so, the benefit and advantage of any and
all homestead, valuation, stay, appraisement, extension or redemption law or
laws now in effect or hereafter enacted, and also waives promptness, diligence,
notice of acceptance, default, dishonor, non-payment, non-performance or any
other notice to or upon the Borrower or the Guarantor.

              (c)       The Guarantor, to the extent he may lawfully and
effectively do so, waives any right now or hereafter existing requiring Lender
as a condition to proceeding against the Guarantor hereunder, to (i) proceed
against the Borrower or any other Person; (ii) proceed against or exhaust any
security held from the Borrower or from any other Person; (iii) pursue any other
remedy in its power; or (iv) accelerate any sums owing Lender or otherwise any
rights or remedies under the Loan Agreement, the Note or any of the other
Financing Documents.

              (d)       Guarantor, to the extent he may legally do so, waives
all rights and benefits under any applicable law purporting to reduce a
guarantor's obligation in proportion to the principal obligation guaranteed, and
any defense based on or arising out of any defense the Borrower may have to
payment and performance under the Loan Agreement, the Note or any of the other
Financing Documents.

              (e)       Guarantor, to the extent he may lawfully and effectively
do so, waives all rights and benefits under any applicable law requiring the
holder or holders of any indebtedness to pursue the primary obligor thereof, any
security which said holder or holders may hold, or any other remedy before
proceeding against the Guarantor.

         SECTION 3.     SCOPE AND DURATION OF GUARANTY. This Guaranty shall
continue in full force and effect until the Borrower or the Guarantor shall have
satisfactorily performed or


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otherwise fully discharged, or caused to be performed or fully discharged, all
of the Obligations.

         SECTION 4.     FREEDOM TO DEAL. Lender shall be at liberty, without
giving notice to or obtaining the assent of the Guarantor or relieving the
Guarantor of any liability hereunder, (a) to amend, modify or supplement any of
the Financing Documents from time to time and (b) to deal with the Borrower in
such manner as it may deem fit; provided the Lender shall not release the
Borrower Collateral (as defined in the Loan Agreement) without the request or
consent of the Guarantor (other than upon satisfaction of the obligations
secured thereby).

         SECTION 5.     DEMAND FOR PERFORMANCE. Any demand for performance by
the Guarantor of its obligations hereunder may be made by Lender on one or more
occasions.

         SECTION 6.     ADDITIONAL WAIVERS BY GUARANTOR. The Guarantor waives
(a) notice of acceptance hereof, (b) notice of any action taken or omitted by
Lender in reliance hereon, (c) any requirement that Lender be diligent or prompt
in making demands hereunder or giving notice to the Guarantor of any default by
the Borrower or asserting any other rights of Lender hereunder against the
Guarantor and (d) any event, occurrence or other circumstances which might
otherwise constitute a legal or equitable discharge of a surety or guarantor
other than full and complete payment (which payment is final and irrevocable
under then applicable bankruptcy and insolvency statutes) and performance of the
Obligations.

         SECTION 7.     WAIVER OF SUBROGATION, ETC. Guarantor hereby
subordinates and agrees not to enforce any claim, right or remedy which
Guarantor may now have or hereafter acquire against the Borrower that arises
hereunder and/or from the performance by Guarantor hereunder, including, without
limitation, any claim, remedy or right of subrogation, reimbursement,
exoneration, indemnification, or participation in any claim, right or remedy of
Lender against the Borrower or any security which Lender now has or may
hereafter acquire, until all obligations of the Borrower to the Lender are
indefeasibly paid in full and Borrower has no further right to borrow funds
under the Financing Documents.

         SECTION 8.     REPRESENTATIONS AND WARRANTIES. Guarantor represents
and warrants to Lender that:

              (a)       AUTHORITY. He has full power, authority and capacity to
enter into this Guaranty, the Pledge Agreement and the other Financing Documents
to which he is a party. No other consent or approval or the taking of any other
action by Guarantor is required as a condition to the validity or enforceability
of this Guaranty, the Pledge Agreement and such other Financing Documents or any
other instrument, document or agreement delivered in connection herewith or
therewith.

              (b)       BINDING AGREEMENTS. This Guaranty, the Pledge Agreement,
the Control Agreement, and the other Financing Documents executed and/or
delivered by Guarantor in connection herewith constitute the valid and legally
binding obligations of Guarantor, enforceable in accordance with their
respective terms, except as enforcement may


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be limited by principles of equity, bankruptcy, insolvency, or other laws
affecting the enforcement of creditors' rights generally.

              (c)       LITIGATION. There are no actions, suits or proceedings
pending against Guarantor before any court or administrative agency, nor are
there any actions, suits or proceedings threatened, which, either in any case or
in the aggregate, would materially and adversely affect the financial condition
or assets of Guarantor, nor are there any such actions, suits or proceedings
which question the validity of this Guaranty, the Pledge Agreement, the Control
Agreement, or any of the other Financing Documents, or any action to be taken in
connection with the transactions contemplated hereby or thereby.

              (d)       NO CONFLICTING LAW OR AGREEMENTS. The execution,
delivery and performance by Guarantor of this Guaranty, the Pledge Agreement,
the Control Agreement, and the other Financing Documents, as the case may be, do
not (i) violate any order, decree or judgment, or any provision of any statute,
rule or regulation; (ii) violate or conflict with, result in a breach of or
constitute (with notice or lapse of time, or both) a default under any
agreement, mortgage, indenture or other contract or undertaking to which he is a
party, or by which his properties or assets are bound; and (iii) result in the
creation or imposition of any lien, charge or encumbrance of any nature
whatsoever upon any property or assets of the Guarantor, except for the liens
granted to Lender.

              (e)       TAXES. He has filed all tax returns which are required
to be filed and all federal, state, municipal and other taxes shown on such
filed returns have been paid.

              (f)       COMPLIANCE. He is not in material default in the payment
or performance of any of his obligations to any third parties or in the
performance of any mortgage, indenture, lease, contract or other agreement to
which he is a party or by which any of its assets or properties are bound.

              (g)       FINANCIAL INFORMATION. All financial information
submitted by Guarantor to Lender, whether previously or in the future, is and
will be true, correct and complete in all material respects.

         SECTION 9.     TRANSFER OF ASSETS. Guarantor agrees that he shall not
during the term of this Guaranty transfer all or substantially all of his assets
to any other Person.

         SECTION 10.    FINANCIAL INFORMATION. Within one hundred twenty (120)
days after the close of each calendar year, Guarantor shall deliver to Lender
(i) annual updates of personal financial statements, and (ii) personal tax
returns prepared by an accountant reasonably acceptable to Lender. Promptly upon
request, Guarantor will provide Lender with such other personal financial
information as Lender may reasonably request.

         SECTION 11.    AMENDMENTS; WAIVERS, ETC. No provision of this Guaranty
may be changed, waived, discharged or terminated except by full performance
thereof or in accordance with the terms of an instrument in writing signed by
the Guarantor and Lender.


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No course of dealing or delay or omission on the part of Lender in exercising
any right shall operate as a waiver thereof or otherwise be prejudicial thereto
except as may be set forth in a writing meeting the requirements of the
preceding sentence.

         SECTION 12.    MISCELLANEOUS. This Guaranty is to be governed by and
construed in accordance with the laws of the State of Connecticut (without
reference to principles of conflicts of law) and shall be binding upon and inure
to the benefit of Guarantor and Lender and their respective heirs, successors
and assigns. It is the intent of each of the parties to this Guaranty that this
Guaranty create a direct obligation of the Guarantor in favor of Lender.

        SECTION 13.     PREJUDGMENT REMEDY WAIVER. THE GUARANTOR ACKNOWLEDGES
THAT THIS GUARANTY AND THE UNDERLYING TRANSACTIONS GIVING RISE HERETO CONSTITUTE
COMMERCIAL TRANSACTIONS WITHIN THE STATE OF CONNECTICUT. THE GUARANTOR HEREBY
EXPRESSLY WAIVES ANY RIGHTS WITH REGARD TO NOTICE AND HEARING UNDER THE
CONNECTICUT GENERAL STATUTES, CHAPTER 903a, AS NOW CONSTITUTED OR HEREAFTER
AMENDED, OR ANY OTHER STATE OR FEDERAL LAW WITH REGARD TO PREJUDGMENT REMEDIES
THAT LENDER MAY DESIRE TO USE, AND FURTHER WAIVES HIS RIGHTS TO REQUEST THE
LENDER POST A BOND, WITH OR WITHOUT SURETY, TO PROTECT BORROWER AGAINST DAMAGES
THAT MAY BE CAUSED BY ANY PREJUDGMENT REMEDY SOUGHT OR OBTAINED BY LENDER. THE
GUARANTOR ACKNOWLEDGES THAT IT MAKES THESE WAIVERS KNOWINGLY, VOLUNTARILY,
WITHOUT DURESS AND ONLY AFTER CONSIDERATION OF THE RAMIFICATIONS OF THESE
WAIVERS WITH HIS ATTORNEYS.

         SECTION 14.    WAIVER OF TRIAL BY JURY. THE GUARANTOR WAIVES TRIAL BY
JURY IN ANY COURT IN ANY SUIT, ACTION, PROCEEDING OR ANY MATTER ARISING IN
CONNECTION WITH OR IN ANY WAY RELATED TO THIS GUARANTY OR THE FINANCING
TRANSACTION OF WHICH THIS GUARANTY IS A PART, OR THE DEFENSE OR ENFORCEMENT OF
ANY OF THE LENDER'S RIGHTS AND REMEDIES IN CONNECTION THEREWITH. THE GUARANTOR
ACKNOWLEDGES THAT IT MAKES THIS WAIVER KNOWINGLY, VOLUNTARILY, WITHOUT DURESS
AND ONLY AFTER CONSIDERATION OF THE RAMIFICATIONS OF THIS WAIVER WITH ITS
ATTORNEYS.

         SECTION 15.    RIGHT TO PURCHASE LOAN. The Guarantor or his nominee
shall have the option, exercisable at any time upon not less than fifteen (15)
days' written notice to the Lender, to purchase all of the Obligations from the
Lender, together with all of Lender's rights in and to the Borrower Collateral
and Collateral. The purchase price therefor shall be the full amount of the
Obligations outstanding at the time of purchase. Such sale by the Lender shall
be without recourse, representation or warranty, other than as to the face
amount of the Obligations and that the Lender has not created any lien, security
interest or encumbrance against its interest in the Obligations.


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         IN WITNESS WHEREOF, the Guarantor has duly executed and delivered this
Guaranty as of the date and year first above written.



                                  /s/ Henry M. Zachs
                                  -----------------------------------------
                                  Henry M. Zachs


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