<PAGE>   1
            As filed with the Securities and Exchange Commission on
                                                    Registration No. 333-_______
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                             ----------------------

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933
                              ---------------------

                                     ISOCOR
             (Exact Name of Registrant as Specified in Its Charter)

                                   California
         (State or Other Jurisdiction of Incorporation or Organization)

                                   95-4310259
                      (I.R.S. Employer Identification No.)

        3420 Ocean Park Boulevard
        Santa Monica, California                                        90405
(Address of Principal Executive Offices)                              (Zip Code)

                              ---------------------



                             1992 STOCK OPTION PLAN
                            (Full Title of the Plan)

                              ---------------------

                                    Paul Gigg
                      President and Chief Executive Officer
                                     ISOCOR
                            3420 Ocean Park Boulevard
                         Santa Monica, California 90405
                    (Name and Address for Agent For Service)

                                 (310) 581-8100
          (Telephone Number, Including Area Code, of Agent For Service)

                              ---------------------


<PAGE>   2


                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
                                                            Proposed Maximum         Proposed Maximum
Title of Securities to be                                  Offering Price Per      Aggregate Offering         Amount of
       Registered             Amount to be Registered            Share                   Price             Registration Fee
<S>                              <C>                          <C>                  <C>                     <C>
Common Stock,
  no par value..........         129,658 shares               $ 3.00 (2)             $   388,974.00            $ 114.75

Common Stock,
  no par value..........         220,342 shares               $ 3.00 (3)             $   661,026.00            $ 195.00

TOTAL                            350,000 shares (1)                                  $ 1,050,000.00            $ 309.75
</TABLE>

(1)    Represents an increase in the number of shares of Common Stock reserved
       for issuance upon the exercise of options issued under the Company's 1992
       Stock Option Plan (the "Plan") of 350,000 shares. The increase was
       approved by the Board of Directors of the Company on February 19, 1998
       and by the shareholders of the Company on May 13, 1998.

(2)    Computed in accordance with Rule 457(h) under the Securities Act of 1933,
       as amended (the "Act") solely for purposes of calculating the
       registration fee. The computation is based on the weighted average
       exercise price of options outstanding under the Plan for which the Common
       Stock issuable upon exercise thereof is being registered hereby.

(3)    Estimated in accordance with Rule 457(h) and 457(c) under the Act solely
       for purposes of calculating the registration fee. The computation is
       based on the closing price of the Company's Common Stock as reported on
       the Nasdaq National Market on August 4, 1998.



<PAGE>   3



PART II: INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3 INCORPORATION OF DOCUMENTS BY REFERENCE

         The following documents and information heretofore filed with the
Securities and Exchange Commission are hereby incorporated by reference:

         ITEM 3 (a)

         The Registrant's Annual Report on Form 10-K filed on March 31, 1998
pursuant to Rule 15(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act").

         ITEM 3 (b)

         The Registrant's Quarterly Report on Form 10-Q filed on May 15, 1998
pursuant to Rule 13(a) of the Exchange Act.

         All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference in this Registration Statement and to be part
hereof from the date of filing of such documents.

         ITEM 3 (c)

         Items 1 and 2 of the Registrant's Registration Statement on Form 8-A
filed on March 5, 1996 pursuant to Section 12 of the Exchange Act.


ITEM 4 DESCRIPTION OF SECURITIES

              Not Applicable.

ITEM 5 INTERESTS OF NAMED EXPERTS AND COUNSEL

         The validity of the Common Stock registered hereby is being passed upon
by Venture Law Group. a Professional Corporation. Certain members of Venture Law
Group, including Elias J. Blawie, Secretary of the Company, beneficially own, in
the aggregate, 8,310 shares of the Company's Common Stock.

ITEM 6 INDEMNIFICATION OF DIRECTORS AND OFFICERS

         The Company has adopted provisions in its Articles of Incorporation
that limit the liability of its directors for monetary damages arising from a
breach of their fiduciary duty as directors to the 


<PAGE>   4

fullest extent permitted by the California Corporations Code. Such limitation of
liability does not affect the availability of equitable remedies such as
injunctive relief or recission.

         The Company's Bylaws provide that the Company shall indemnify its
directors and officers to the fullest extent permitted by California law,
including circumstances in which indemnification is otherwise discretionary
under California law. The Company has entered into indemnification agreements
with its directors and officers containing provisions which are, in some
respects, broader than the specific indemnification provisions contained in the
California Corporations Code. The indemnification agreements may require the
Company, among other things, to indemnify its directors and officers against
certain liabilities that may arise by reason of their status or service as
directors or officers (other than liabilities arising from willful misconduct of
a culpable nature), to advance their expenses as incurred as a result of any
proceeding against them as to which they could be indemnified and to obtain
directors' and officers' insurance, if available on reasonable terms. The
Company has obtained such directors' and officers' insurance.

         At present, there is no pending litigation or proceeding involving any
director, officer, employee or agent of the Company where indemnification would
be required or permitted. The Company is not aware of any threatened litigation
or proceeding which might result in a claim for such indemnification.

ITEM 7 EXEMPTION FROM REGISTRATION CLAIMED

             Not Applicable.

ITEM 8 EXHIBITS

<TABLE>
<CAPTION>
        Exhibit
        Number             Document
        ------             --------

<S>        <C>             <C>                                       
           4.1             1992 Stock Option Plan and forms of option agreement for 
                           use with plan.
           5.1             Opinion of Venture Law Group, A Professional Corporation,
                           as to legality of securities being registered.
          23.1             Consent of Counsel (contained in Exhibit 5.1 hereto).
          23.2             Consent of Independent Accountants (see page 8).
          24.1             Power of Attorney (see page 7).
</TABLE>


ITEM 9 UNDERTAKINGS

           A.     The undersigned Registrant hereby undertakes:

                  (1) To file during any period in which offers or sales are
being made, a post-effective amendment to this Registration statement to include
any material information with respect 


<PAGE>   5

to the plan of distribution not previously disclosed in the Registration
Statement or any material change to such information in the Registration
Statement.

                  (2) That, for the purpose of determining any liability under
the Securities Act, each such post-effective amendment shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

                  (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         B. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and where applicable each filing of an employee
benefit plan's annual report pursuant to Section 15(d) of the Securities
Exchange Act of 1934) that is incorporated by reference in the Registration
Statement shall be deemed to be a new registration statement relating to the
securities offered therein, and the offering of such securities at that time
shall be deemed to be the initial bona fide offering thereof.

         C. Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.



<PAGE>   6


                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant, ISOCOR, a corporation organized and existing under the laws of the
State of California, certifies that it has reasonable grounds to believe that it
meets all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Santa Monica, State of California, on this 11th
day of August, 1998.

                                        ISOCOR


                                        By:  /s/ PAUL GIGG
                                             -----------------------------------
                                             Paul Gigg, President and
                                             Chief Executive Officer

                                POWER OF ATTORNEY

         KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Paul Gigg and Janine M. Bushman, jointly
and severally, his or her attorneys-in-fact, each with the power of
substitution, for him or her in any and all capacities, to sign any amendments
to this Registration Statement on Form S-8, and to file the same, with exhibits
thereto and other documents in connection therewith, with the Securities and
Exchange Commission, hereby ratifying and confirming all that each of said
attorneys-in-fact, or his or her substitute or substitutes, may do or cause to
be done by virtue hereof.

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.


<TABLE>
<CAPTION>
          Signature                                     Title                                  Date
--------------------------------        --------------------------------------               --------
<S>                                     <C>                                              <C>
                                        
/s/       PAUL GIGG                     President, Chief Executive Officer and            August 11, 1998
--------------------------------        Director (Principal Executive Officer)
         (Paul Gigg)

                                        
/s/   JANINE M. BUSHMAN                 Vice President, Finance and                       August 11, 1998
--------------------------------        Administration, Chief Financial  Officer
     (Janine M. Bushman)                and Director (Principal Financial and
                                        Accounting Officer)

/s/      DENNIS CAGAN                   Director                                          August 11, 1998
--------------------------------
        (Dennis Cagan)

                                        Chairman of the Board of Directors and            August 11, 1998
/s/      ANDREW DEMARI                  Director
--------------------------------
       (Andrew De Mari)


/s/   ALEXANDRA GIURGIU                 Director                                          August 11, 1998
--------------------------------
     (Alexandra Giurgiu)

/s/   G. BRADFORD JONES                 Director                                          August 11, 1998
--------------------------------
     (G. Bradford Jones)

/s/     WILLIAM YUNDT                   Director                                          August 11, 1998
--------------------------------
       (William Yundt)

</TABLE>

<PAGE>   7

                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

--------------------------------------------------------------------------------


                                    EXHIBITS

--------------------------------------------------------------------------------

                       Registration Statement on Form S-8

                                     ISOCOR


                                August 11, 1998

<PAGE>   8


                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>
Exhibit
Number

<S>           <C>                                                                     
  4.1         1992 Stock Option Plan and forms of option agreements for use with plan.

  5.1         Opinion of Venture Law Group, A Professional Corporation, as to legality
              of securities being registered

 23.1         Consent of Counsel (contained in Exhibit 5.1 hereto).

 23.2         Consent of Independent Auditors.

 24.1         Power of Attorney.

</TABLE>
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 15501}]
{"company-data": {"conformed-name": "ISOCOR", "cik": "0000879283", "assigned-sic": "7372", "irs-number": "954310259", "state-of-incorporation": "CA", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-61133", "film-number": "98681669"}, "business-address": {"street1": "3420 OCEAN PARK BLVD", "city": "SANTA MONICA", "state": "CA", "zip": "90405"}, "mail-address": {"street2": "3420 OCEAN PARK BLVD SUITE 2010", "city": "SANTA MONICA", "state": "CA", "zip": "904053306"}}
1
            As filed with the Securities and Exchange Commission on
                                                    Registration No. 333-_______
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                             ----------------------

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933
                              ---------------------

                                     ISOCOR
             (Exact Name of Registrant as Specified in Its Charter)

                                   California
         (State or Other Jurisdiction of Incorporation or Organization)

                                   95-4310259
                      (I.R.S. Employer Identification No.)

        3420 Ocean Park Boulevard
        Santa Monica, California                                        90405
(Address of Principal Executive Offices)                              (Zip Code)

                              ---------------------

                             1992 STOCK OPTION PLAN
                            (Full Title of the Plan)

                              ---------------------

                                    Paul Gigg
                      President and Chief Executive Officer
                                     ISOCOR
                            3420 Ocean Park Boulevard
                         Santa Monica, California 90405
                    (Name and Address for Agent For Service)

                                 (310) 581-8100
          (Telephone Number, Including Area Code, of Agent For Service)

                              ---------------------
2

                         CALCULATION OF REGISTRATION FEE
Proposed Maximum         Proposed Maximum
Title of Securities to be                                  Offering Price Per      Aggregate Offering         Amount of
       Registered             Amount to be Registered            Share                   Price             Registration Fee
Common Stock,
  no par value..........         129,658 shares               $ 3.00 (2)             $   388,974.00            $ 114.75

Common Stock,
  no par value..........         220,342 shares               $ 3.00 (3)             $   661,026.00            $ 195.00

TOTAL                            350,000 shares (1)                                  $ 1,050,000.00            $ 309.75
(1)    Represents an increase in the number of shares of Common Stock reserved
       for issuance upon the exercise of options issued under the Company's 1992
       Stock Option Plan (the "Plan") of 350,000 shares. The increase was
       approved by the Board of Directors of the Company on February 19, 1998
       and by the shareholders of the Company on May 13, 1998.

(2)    Computed in accordance with Rule 457(h) under the Securities Act of 1933,
       as amended (the "Act") solely for purposes of calculating the
       registration fee. The computation is based on the weighted average
       exercise price of options outstanding under the Plan for which the Common
       Stock issuable upon exercise thereof is being registered hereby.

(3)    Estimated in accordance with Rule 457(h) and 457(c) under the Act solely
       for purposes of calculating the registration fee. The computation is
       based on the closing price of the Company's Common Stock as reported on
       the Nasdaq National Market on August 4, 1998.
3

PART II: INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3 INCORPORATION OF DOCUMENTS BY REFERENCE

         The following documents and information heretofore filed with the
Securities and Exchange Commission are hereby incorporated by reference:

         ITEM 3 (a)

         The Registrant's Annual Report on Form 10-K filed on March 31, 1998
pursuant to Rule 15(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act").

         ITEM 3 (b)

         The Registrant's Quarterly Report on Form 10-Q filed on May 15, 1998
pursuant to Rule 13(a) of the Exchange Act.

         All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference in this Registration Statement and to be part
hereof from the date of filing of such documents.

         ITEM 3 (c)

         Items 1 and 2 of the Registrant's Registration Statement on Form 8-A
filed on March 5, 1996 pursuant to Section 12 of the Exchange Act.

ITEM 4 DESCRIPTION OF SECURITIES

              Not Applicable.

ITEM 5 INTERESTS OF NAMED EXPERTS AND COUNSEL

         The validity of the Common Stock registered hereby is being passed upon
by Venture Law Group. a Professional Corporation. Certain members of Venture Law
Group, including Elias J. Blawie, Secretary of the Company, beneficially own, in
the aggregate, 8,310 shares of the Company's Common Stock.

ITEM 6 INDEMNIFICATION OF DIRECTORS AND OFFICERS

         The Company has adopted provisions in its Articles of Incorporation
that limit the liability of its directors for monetary damages arising from a
breach of their fiduciary duty as directors to the
4

fullest extent permitted by the California Corporations Code. Such limitation of
liability does not affect the availability of equitable remedies such as
injunctive relief or recission.

         The Company's Bylaws provide that the Company shall indemnify its
directors and officers to the fullest extent permitted by California law,
including circumstances in which indemnification is otherwise discretionary
under California law. The Company has entered into indemnification agreements
with its directors and officers containing provisions which are, in some
respects, broader than the specific indemnification provisions contained in the
California Corporations Code. The indemnification agreements may require the
Company, among other things, to indemnify its directors and officers against
certain liabilities that may arise by reason of their status or service as
directors or officers (other than liabilities arising from willful misconduct of
a culpable nature), to advance their expenses as incurred as a result of any
proceeding against them as to which they could be indemnified and to obtain
directors' and officers' insurance, if available on reasonable terms. The
Company has obtained such directors' and officers' insurance.

         At present, there is no pending litigation or proceeding involving any
director, officer, employee or agent of the Company where indemnification would
be required or permitted. The Company is not aware of any threatened litigation
or proceeding which might result in a claim for such indemnification.

ITEM 7 EXEMPTION FROM REGISTRATION CLAIMED

             Not Applicable.

ITEM 8 EXHIBITS
Exhibit
        Number             Document
        ------             --------
4.1             1992 Stock Option Plan and forms of option agreement for 
                           use with plan.
           5.1             Opinion of Venture Law Group, A Professional Corporation,
                           as to legality of securities being registered.
          23.1             Consent of Counsel (contained in Exhibit 5.1 hereto).
          23.2             Consent of Independent Accountants (see page 8).
          24.1             Power of Attorney (see page 7).
ITEM 9 UNDERTAKINGS

           A.     The undersigned Registrant hereby undertakes:

                  (1) To file during any period in which offers or sales are
being made, a post-effective amendment to this Registration statement to include
any material information with respect
5

to the plan of distribution not previously disclosed in the Registration
Statement or any material change to such information in the Registration
Statement.

                  (2) That, for the purpose of determining any liability under
the Securities Act, each such post-effective amendment shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

                  (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         B. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Securities Exchange Act of 1934 (and where applicable each filing of an employee
benefit plan's annual report pursuant to Section 15(d) of the Securities
Exchange Act of 1934) that is incorporated by reference in the Registration
Statement shall be deemed to be a new registration statement relating to the
securities offered therein, and the offering of such securities at that time
shall be deemed to be the initial bona fide offering thereof.

         C. Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.
6

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant, ISOCOR, a corporation organized and existing under the laws of the
State of California, certifies that it has reasonable grounds to believe that it
meets all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Santa Monica, State of California, on this 11th
day of August, 1998.

                                        ISOCOR

                                        By:  /s/ PAUL GIGG
                                             -----------------------------------
                                             Paul Gigg, President and
                                             Chief Executive Officer

                                POWER OF ATTORNEY

         KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Paul Gigg and Janine M. Bushman, jointly
and severally, his or her attorneys-in-fact, each with the power of
substitution, for him or her in any and all capacities, to sign any amendments
to this Registration Statement on Form S-8, and to file the same, with exhibits
thereto and other documents in connection therewith, with the Securities and
Exchange Commission, hereby ratifying and confirming all that each of said
attorneys-in-fact, or his or her substitute or substitutes, may do or cause to
be done by virtue hereof.

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.
Signature                                     Title                                  Date
--------------------------------        --------------------------------------               --------
/s/       PAUL GIGG                     President, Chief Executive Officer and            August 11, 1998
--------------------------------        Director (Principal Executive Officer)
         (Paul Gigg)

                                        
/s/   JANINE M. BUSHMAN                 Vice President, Finance and                       August 11, 1998
--------------------------------        Administration, Chief Financial  Officer
     (Janine M. Bushman)                and Director (Principal Financial and
                                        Accounting Officer)

/s/      DENNIS CAGAN                   Director                                          August 11, 1998
--------------------------------
        (Dennis Cagan)

                                        Chairman of the Board of Directors and            August 11, 1998
/s/      ANDREW DEMARI                  Director
--------------------------------
       (Andrew De Mari)

/s/   ALEXANDRA GIURGIU                 Director                                          August 11, 1998
--------------------------------
     (Alexandra Giurgiu)

/s/   G. BRADFORD JONES                 Director                                          August 11, 1998
--------------------------------
     (G. Bradford Jones)

/s/     WILLIAM YUNDT                   Director                                          August 11, 1998
--------------------------------
       (William Yundt)
7

                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

--------------------------------------------------------------------------------

                                    EXHIBITS

--------------------------------------------------------------------------------

                       Registration Statement on Form S-8

                                     ISOCOR

                                August 11, 1998
8

                                INDEX TO EXHIBITS
Exhibit
Number
4.1         1992 Stock Option Plan and forms of option agreements for use with plan.

  5.1         Opinion of Venture Law Group, A Professional Corporation, as to legality
              of securities being registered

 23.1         Consent of Counsel (contained in Exhibit 5.1 hereto).

 23.2         Consent of Independent Auditors.

 24.1         Power of Attorney.