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                                                                     EXHIBIT 4.3



                                     ISOCOR

                             1999 STOCK OPTION PLAN

                          NOTICE OF STOCK OPTION GRANT

Optionee's Name and Address:

<<Optionee>>

         You have been granted an option to purchase Common Stock of ISOCOR (the
"Company") as follows:

         Board Approval Date:                        <<BoardApprovalDate>>

         Date of Grant (Later of Board
              Approval Date or
              Commencement of
              Employment/Consulting):                <<GrantDate>>

         Exercise Price Per Share:                   <<ExercisePrice>>

         Total Number of Shares Granted:             <<NoofShares>>

         Total Price of Shares Granted:              <<TotalExercisePrice>>

         Type of Option:                             <<NoSharesISO>> Shares
                                                     Incentive Stock Option

                                                     <<NoSharesNSO>> Shares
                                                     Nonstatutory Stock Option

         Term/Expiration Date:                       <<ExpirDate>>

         Vesting Commencement Date:                  <<VestingStartDate>>

         Vesting Schedule:                           1/4 of the original Shares
                                                     subject to this Option
                                                     shall vest one year after
                                                     the Vesting Commencement
                                                     Date and 1/48th of the
                                                     original number of Shares
                                                     subject to this Option
                                                     shall vest each month
                                                     thereafter.

         Termination Period:                         This Option may be
                                                     exercised for a period of
                                                     45 days after termination
                                                     of employment or consulting
                                                     relationship except as set
                                                     out in Sections 7 and 8 of
                                                     the Stock Option Agreement
                                                     (but in no event later than
                                                     the Expiration Date).

         By your signature and the signature of the Company's representative
below, you and the Company agree that this Option is granted under and governed
by the terms and conditions of the ISOCOR 1999 Stock Option Plan and the Stock
Option Agreement, all of which are attached and made a part of this document.



OPTIONEE:                                     ISOCOR


- --------------------------------              By:
Signature                                        ------------------------------


- --------------------------------              Title:
Print Name                                          ---------------------------



                                                     (C) 1996 Venture Law Group

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                                     ISOCOR

                             STOCK OPTION AGREEMENT



         1. GRANT OF OPTION. ISOCOR, a California corporation (the "Company"),
hereby grants to the Optionee named in the Notice of Stock Option Grant attached
to this Agreement ("Optionee"), an option (the "Option") to purchase the total
number of shares of Common Stock (the "Shares") set forth in the Notice of Stock
Option Grant, at the exercise price per share set forth in the Notice of Stock
Option Grant (the "Exercise Price") subject to the terms, definitions and
provisions of the 1999 Stock Option Plan (the "Plan") adopted by the Company,
which is incorporated in this Agreement by reference. In the event of a conflict
between the terms of the Plan and the terms of this Agreement, the terms of the
Plan shall govern. Unless otherwise defined in this Agreement, the terms used in
this Agreement shall have the meanings defined in the Plan.

         To the extent designated an Incentive Stock Option in the Notice of
Stock Option Grant, this Option is intended to qualify as an Incentive Stock
Option as defined in Section 422 of the Internal Revenue Code of 1986, as
amended (the "Code") and, to the extent not so designated, this Option is
intended to be a Nonstatutory Stock Option.

         2. EXERCISE OF OPTION. This Option shall be exercisable during its term
in accordance with the Vesting Schedule set out in the Notice of Stock Option
Grant and with the provisions of Sections 9 and 10 of the Plan as follows:

            (a) RIGHT TO EXERCISE.

                (i) This Option may not be exercised for a fraction of a share.

                (ii) In the event of Optionee's death, disability or other
termination of employment, the exercisability of the Option is governed by
Sections 6, 7 and 8 below, subject to the limitations contained in paragraphs
(iii) and (iv) below.

                (iii) In no event may this Option be exercised after the date of
expiration of the term of this Option as set forth in the Notice of Stock Option
Grant.

                (iv) If designated an Incentive Stock Option in the Notice of
Stock Option Grant, in the event that the Shares subject to this Option (and all
other Incentive Stock Options granted to Optionee by the Company or any Parent
or Subsidiary) that vest in any calendar year have an aggregate fair market
value (determined for each Share as of the Date of Grant of the option covering
such Share) in excess of $100,000, the Shares in excess of $100,000 shall be
treated as subject to a Nonstatutory Stock Option, in accordance with Section 5
of the Plan.

            (b) METHOD OF EXERCISE.

                (i) This Option shall be exercisable by delivering to the
Company a written notice of exercise (in the form attached as Exhibit A) which
shall state the election to exercise the Option, the number of Shares in respect
of which the Option is being exercised, and such other representations and
agreements as to the holder's investment intent with respect to such Shares of
Common Stock as may be required by the Company pursuant to the provisions of the
Plan. Such written notice shall be signed by Optionee and shall be delivered in
person or by certified mail to the Stock Option Administrator of the Company.
The written notice shall be accompanied by payment of the exercise price. This
Option shall be deemed to be exercised upon receipt by the Company of such
written notice accompanied by the exercise price.


                                                      (C) 1996 Venture Law Group

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                (ii) As a condition to the exercise of this Option, Optionee
agrees to make adequate provision for federal, state or other tax withholding
obligations, if any, which arise upon the exercise of the Option or disposition
of Shares, whether by withholding, direct payment to the Company, or otherwise.

                (iii) No Shares will be issued pursuant to the exercise of an
Option unless such issuance and such exercise shall comply with all relevant
provisions of law and the requirements of any stock exchange upon which the
Shares may then be listed. Assuming such compliance, for income tax purposes the
Shares shall be considered transferred to Optionee on the date on which the
Option is exercised with respect to such Shares.

         3. OPTIONEE'S REPRESENTATIONS. In the event the Shares purchasable
pursuant to the exercise of this Option have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), at the time this
Option is exercised, Optionee shall, if required by the Company, concurrently
with the exercise of all or any portion of this Option, deliver to the Company
an investment representation statement in customary form, a copy of which is
available for Optionee's review from the Company upon request.

         4. METHOD OF PAYMENT. Payment of the exercise price shall be by any of
the following, or a combination of the following, at the election of Optionee:
(a) cash; (b) check; (c) surrender of other shares of Common Stock of the
Company that (i) either have been owned by Optionee for more than six (6) months
on the date of surrender or were not acquired, directly or indirectly, from the
Company, or (ii) have a Fair Market Value on the date of surrender equal to the
aggregate exercise price of the Shares as to which said Option shall be
exercised; or (d) if there is a public market for the Shares and they are
registered under the Securities Act, delivery of a properly executed exercise
notice together with irrevocable instructions to a broker to deliver promptly to
the Company the amount of sale or loan proceeds required to pay the exercise
price.

         5. RESTRICTIONS ON EXERCISE. This Option may not be exercised until
such time as the Plan has been approved by the shareholders of the Company, or
if the issuance of such Shares upon such exercise or the method of payment of
consideration for such shares would constitute a violation of any applicable
federal or state securities or other law or regulation, including any rule under
Part 207 of Title 12 of the Code of Federal Regulations ("Regulation G") as
promulgated by the Federal Reserve Board. As a condition to the exercise of this
Option, the Company may require Optionee to make any representation and warranty
to the Company as may be required by any applicable law or regulation.

         6. TERMINATION OF RELATIONSHIP. In the event of termination of
Optionee's Continuous Status as an Employee or Consultant, Optionee may, to the
extent otherwise so entitled at the date of such termination (the "Termination
Date"), exercise this Option during the Termination Period set out in the Notice
of Stock Option Grant. To the extent that Optionee was not entitled to exercise
this Option at the date of such termination, or if Optionee does not exercise
this Option within the time specified in the Notice of Stock Option Grant, the
Option shall terminate.

         7. DISABILITY OF OPTIONEE. Notwithstanding the provisions of Section 6
above, in the event of termination of Optionee's Continuous Status as an
Employee or or Consultant with the Company as a result of total and permanent
disability (as defined in Section 22(e)(3) of the Code), Optionee may, but only
within twelve (12) months from the date of termination of employment or
consultancy (but in no event later than the date of expiration of the term of
this Option as set forth in Section 10 below), exercise the Option to the extent
otherwise so entitled at the date of such termination. To the extent that
Optionee was not entitled to exercise the Option at the date of termination, or
if Optionee does not exercise such Option (to the extent otherwise so entitled)
within the time specified in this Agreement, the Option shall terminate.

         8. DEATH OF OPTIONEE. In the event of the death of Optionee, the Option
may be exercised, at any time within six (6) months following the date of death
(but in no event later than the date of expiration of the term of this Option as
set forth in Section 10 below), by Optionee's estate or by a person who acquired
the right to exercise the Option by bequest or inheritance, but only to the
extent of the right to exercise that had accrued at the date of death.




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         9. NON-TRANSFERABILITY OF OPTION. This Option may not be transferred in
any manner otherwise than by will or by the laws of descent or distribution. The
designation of a beneficiary does not constitute a transfer. An Option may be
exercised during the lifetime of Optionee only by Optionee or a transferee
permitted by this section. The terms of this Option shall be binding upon the
executors, administrators, heirs, successors and assigns of Optionee.

         10. TERM OF OPTION. This Option may be exercised only within the term
set out in the Notice of Stock Option Grant, and may be exercised during such
term only in accordance with the Plan and the terms of this Option.

         11. NO ADDITIONAL EMPLOYMENT RIGHTS. Optionee understands and agrees
that the vesting of Shares pursuant to the Vesting Schedule is earned only by
continuing as an Employee or Consultant at the will of the Company (not through
the act of being hired, being granted this Option or acquiring Shares under this
Agreement). Optionee further acknowledges and agrees that nothing in this
Agreement, nor in the Plan which is incorporated in this Agreement by reference,
shall confer upon Optionee any right with respect to continuation as an Employee
or Consultant with the Company, nor shall it interfere in any way with his or
her right or the Company's right to terminate his or her employment or
consulting relationship at any time, with or without cause.

         12. TAX CONSEQUENCES. Optionee acknowledges that he or she has read the
brief summary set forth below of certain federal tax consequences of exercise of
this Option and disposition of the Shares under the law in effect as of the date
of grant. OPTIONEE UNDERSTANDS THAT THIS SUMMARY IS NECESSARILY INCOMPLETE, AND
THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE. OPTIONEE SHOULD CONSULT HIS
OR HER OWN TAX ADVISER BEFORE EXERCISING THIS OPTION OR DISPOSING OF THE SHARES.

            (a) EXERCISE OF INCENTIVE STOCK OPTION. If this Option is an
Incentive Stock Option, there will be no regular federal income tax liability
upon the exercise of the Option, although the excess, if any, of the fair market
value of the Shares on the date of exercise over the Exercise Price will be
treated as an item of alternative minimum taxable income for federal tax
purposes and may subject Optionee to the alternative minimum tax in the year of
exercise.

            (b) EXERCISE OF NONSTATUTORY STOCK OPTION. If this Option does not
qualify as an Incentive Stock Option, Optionee may incur regular federal income
tax liability upon the exercise of the Option. Optionee will be treated as
having received compensation income (taxable at ordinary income tax rates) equal
to the excess, if any, of the fair market value of the Shares on the date of
exercise over the exercise price. In addition, if Optionee is an employee of the
Company, the Company will be required to withhold from Optionee's compensation
or collect from Optionee and pay to the applicable taxing authorities an amount
equal to a percentage of this compensation income at the time of exercise.

            (c) DISPOSITION OF SHARES. If this Option is an Incentive Stock
Option and if Shares transferred pursuant to the Option are held for more than
one year after exercise and more than two years after the Date of Grant, any
gain realized on disposition of the Shares will be treated as long-term capital
gain for federal income tax purposes. If Shares purchased under an Incentive
Stock Option are disposed of before the end of either of such two holding
periods, then any gain realized on such disposition will be treated as
compensation income (taxable at ordinary income rates) to the extent of the
excess, if any, of the lesser of (i) the fair market value of the Shares on the
date of exercise, or (ii) the sales proceeds, over the exercise price. If this
Option is a Nonstatutory Stock Option, then gain realized on the disposition of
Shares will be treated as long-term or short-term capital gain depending on
whether or not the disposition occurs more than one year after the exercise
date. In the case of either an Incentive Stock Option or a Nonstatutory Stock
Option, the long-term capital gain will be taxed for federal income tax and
alternative minimum tax purposes at a maximum rate of 20%.

            (d) NOTICE OF DISQUALIFYING DISPOSITION. If the Option granted to
Optionee in this Agreement is an Incentive Stock Option, and if Optionee sells
or otherwise disposes of any of the Shares acquired pursuant to the Incentive
Stock Option on or before the later of (i) the date two years after the Date of
Grant, or



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(ii) the date one year after transfer of such Shares to Optionee upon exercise
of the Incentive Stock Option, Optionee shall notify the Company in writing
within thirty (30) days after the date of any such disposition. Optionee agrees
that Optionee may be subject to income tax withholding by the Company on the
compensation income recognized by Optionee from the early disposition by payment
in cash or out of the current earnings paid to Optionee.

         13. SIGNATURE. This Stock Option Agreement shall be deemed executed by
the Company and Optionee upon execution by such parties of the Notice of Stock
Option Grant attached to this Stock Option Agreement.

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                                    EXHIBIT A

                               NOTICE OF EXERCISE



To:            ISOCOR
Attn:          Stock Option Administrator
Subject:       Notice of Intention to Exercise Stock Option

         This is official notice that the undersigned ("Optionee") intends to
exercise Optionee's option to purchase __________ shares of ISOCOR Common Stock,
under and pursuant to the Company's 1999 Stock Option Plan and the Notice of
Stock Option Grant and Stock Option Agreement dated ___________, as follows:


               Date of Grant :         ____________________

               Number of Shares:       ____________________

               Purchase Price:         ____________________

               Method of Payment
               of Purchase Price:      ____________________

      Social Security No.: ________________________________

      The shares should be issued as follows:

               Name:     __________________________________

               Address:  __________________________________

                         __________________________________

                         __________________________________

               Signed:   __________________________________

               Date:     __________________________________