Important Notice Regarding Availability of Proxy Materials

for the 20162019 Annual Meeting of Stockholders to be Held on June 13, 2016

12, 2019

names that are beneficially owned by others so that they may forward this solicitation material to such beneficial owners. In addition, we may reimburse such persons for costs incurred in forwarding the solicitation materials to such beneficial owners. The original solicitation of proxies by mail may be supplemented by a solicitation by telephone, e-mail or other means by our directors, officers or employees. No additional compensation will be paid to these individuals for soliciting. We intend to post this proxy statement and our 20152018 Annual Report on Form 10-K on our website (http://investor.stamps.com/sec.cfm) for public review. Except as described above, we do not presently intend to solicit proxies other than by mail. We have no present plans to hire special employees or paid solicitors to assist in obtaining proxies, but reserve the option to do so. For our 2015 Annual Meeting last year, we initially had no plans to hire solicitors to assist in obtaining proxies. However, we ultimately engaged a company to provide advisory and consulting services and to act as proxy solicitor in connection with such meeting, at a cost of approximately $25,000 plus expenses. If we do hire solicitors for the 2016 Annual Meeting, the arrangement may or may not be similar to what we did last year.

PROPOSAL ONE: ELECTION OF DIRECTOR

DIRECTORS

M.S. in Aeronautics from the California Institute of Technology, his Ph.D. in Astrodynamics and Control from University of California, Los Angeles, and his J.D. from the University of West Los Angeles. Mr. Ananda was instrumental in the founding of our company and has extensive experience with the technology and industry of our PC Postage business, and that experience has proven invaluable for our Board.

BOARD COMMITTEES AND MEETINGS AND CORPORATE GOVERNANCE

members of management. Upon

Code of Ethics

Topic 718, Compensation—Stock Compensation (“ASC 718”). See Note 2 of our “Notes to Consolidated Financial Statements” in our annual report on Form 10-K filed with the Securities and Exchange Commission on February 29, 2016 for a discussion of assumptions we made in determining the amounts included in this column. For each director, the aggregate grant date fair value in this column is equal to the individual grant date fair value of the options to purchase 5,000 shares of common stock granted on June 17, 2015, as directors received only one grant of options during 2015.

PROPOSAL TWO: ADVISORY VOTE ON EXECUTIVE COMPENSATION

PROPOSAL THREE: 2016 AMENDMENT TO STAMPS.COM INC. 2010 EQUITY INCENTIVE PLAN

General

We are asking stockholders to approve an amendment (the “2016 Amendment”) to the Stamps.com Inc. 2010 Equity Incentive Plan (the “2010 Plan”), which 2016 Amendment was adopted by our Board on April 28, 2016, subject to such stockholder approval. The 2016 Amendment increases the maximum aggregate number of shares of common stock and stock equivalents available for issuance pursuant to awards under the 2010 Plan by an additional one million two hundred thousand (1,200,000) shares. Except for this increase in the number of shares available for awards, the 2010 Plan otherwise remains unchanged by the 2016 Amendment.

Prior to the 2016 Amendment only 293,798 shares remained available for awards under the 2010 Plan as of April 18, 2016. The 2016 Amendment was adopted by our Board (i) in order to recognize and provide equity incentives to continue to drive our strong growth and performance, as evidenced by a substantial increase in our market capitalization, revenue and adjusted EBITDA, and the successful completion of the ShipStation®, ShipWorks® and Endicia® acquisitions, which were completed in June 2014, August 2014 and November 2015, respectively; and (ii) to continue to have sufficient awards available for grant to our employees and directors, consistent with the factors described in the Compensation Discussion and Analysis provided with this Proxy Statement. Those factors include: the individual’s position and scope of responsibility; the vesting period (and thus, retention value) remaining on the grantee’s previously granted options; the grantee’s ability to affect profitability and stockholder value; the grantee’s historic and recent job performance; equity compensation for similar positions at comparable companies; and the value of stock options in relation to other elements of total compensation.

We believe that a cost-effective and competitive equity compensation program that includes awards that have not yet vested, is essential for recruiting, motivating, and retaining talented employees, including our executive managers and named executive officers. For this reason, combined with the other factors listed above, our Board approved the 2016 Amendment on April 28, 2016.

As required by the applicable NASDAQ rules, the 2016 Amendment will not become effective unless it is approved by our stockholders.

Key Considerations

In its determination to approve the 2016 Amendment, our Board reviewed an analysis prepared by our management that included the following:

The following paragraphs include additional information to help assess the potential dilutive impact of awards under the 2010 Plan.

The 1,200,000 shares requested to be provided under the 2016 Amendment in this Proposal 3 represent 6.87% of the 17,456,552 issued and outstanding shares as of April 18, 2016.

The following table sets forth additional relevant information about all of our outstanding awards and available shares under all of our equity plans with outstanding or available awards, all of which plans have been approved by our stockholders:

The 2010 Plan, the 2016 Amendment of which is on the ballot for this annual meeting, is the only active plan that can be used for future equity grants. Nonetheless, at April 18, 2016, option awards under our 1999 Plan remained outstanding which are exercisable to purchase an aggregate of 40,957 shares of our common stock.

Our Board believes the 1,200,000 additional authorized shares to be made available for grants of awards under the 2016 Amendment represents reasonable potential equity dilution and provides management with an appropriate equity plan with which to satisfactorily align the incentives of our employees, directors and other eligible participants to increase the value of our company for all stockholders.

The inclusion of this information in this Proxy Statement should not be regarded as an indication that the assumptions used to determine the number of shares will be predictive of actual future equity grants. These assumptions are forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements involve risks and uncertainties that could cause actual outcomes to differ materially from those in the forward-looking statements, including our ability to attract and retain talent, achievement of performance metrics with respect to certain equity-based awards, the extent of option exercise activity, and others, including those described in our Form 10-K for the year ended December 31, 2015.

Highlights of the 2016 Amendment

The 2016 Amendment increases the maximum aggregate number of shares of stock and stock equivalents authorized for issuance under the 2010 Plan by 1,200,000 shares, subject to stockholder approval of the 2016 Amendment to the 2010 Plan.

As of April 18, 2016, and excluding the effects of the 2016 Amendment, approximately 293,798 shares of stock remain available for future grants of awards under the 2010 Plan, calculated as follows:

If stockholders approve the 2016 Amendment, 1,493,798 shares of stock will be available for new grants under the 2010 Plan, as amended.

Summary of the 2010 Equity Incentive Plan

The 2010 Plan contains the following important features:

• Repricing of stock options and stock appreciation rights is prohibited unless stockholder approval is obtained.

• Stock options and stock appreciation rights must be granted with an exercise price that is not less than 100% of the fair market value on the date of grant.

• Automatic replacement of stock options or stock appreciation rights when a stock option or stock appreciation right is exercised with previously acquired shares of our common stock (so-called “reloading”) is not permitted.

• The 2010 Plan has a ten-year term that ends June 16, 2020.

• If an award expires unexercised, or is forfeited, canceled, reacquired by us at cost, satisfied without issuance of stock or payment of cash or is otherwise terminated without being exercised, the unvested or cancelled shares will be returned to the available pool of shares for future awards.

• No more than 700,000 shares and share equivalents may be granted to any one participant in a calendar year.

• “Full value” awards (such as restricted stock and restricted stock units) are counted against the 2010 Plan overall limits as two shares (rather than one), while options and stock appreciation rights are counted as one share.

Administration. The 2010 Plan is administered by the Compensation Committee of our Board. Subject to the provisions of the 2010 Plan, the Compensation Committee has full power and authority to select the participants to whom awards will be granted, to determine (and modify) the specific terms and conditions of each award, including the conditions for the vesting, performance goals and exercisability of the award, and to interpret the 2010 Plan and adopt, amend, or rescind rules, procedures, agreements, and forms relating to the 2010 Plan.

Eligibility. Employees, directors, and third party service providers are eligible to receive awards, although third party service providers and outside directors are not eligible for incentive stock options. The Compensation Committee has the discretion to select the employees, directors, and third party service providers to whom awards will be granted. As of April 18, 2016, we had approximately 585 employees, 3 non-employee directors and 1 consultant who were eligible to participate in the 2010 Plan. The actual number of individuals or entities who will receive awards cannot be determined in advance because the Compensation Committee has the discretion to select the award recipients.

Types of Awards. The following is a brief summary of the types of awards that may be granted:

Stock Options. A stock option (either an incentive stock option or a nonstatutory stock option) entitles the participant to purchase shares of our common stock at specified times at an exercise price set on the grant date. A participant has no rights as a stockholder with respect to any shares covered by the option until the option is exercised by the participant and shares are issued by us. At the time of grant, the Compensation Committee will determine such matters as: (a) whether the award will be an incentive stock option or a nonstatutory stock option; (b) the number of underlying shares; (c) the exercise price, which may not be less than 100% of the fair market value of a share on the grant date; (d) the vesting schedule; and (e) the term of the option, which may not exceed 10 years from the grant date.

Stock Appreciation Right (“SAR”). An SAR is an award entitling the participant to receive cash or shares, or a combination thereof, with a value equal to any increase in the value of our shares from the date of grant to the date of exercise. The amount of the award to be paid on an exercise date is determined by multiplying the number of shares for which the SAR is exercised by the excess of the fair market value of a share on the date of exercise over the per share exercise price. For cash-settled SARs, the participant will have no rights as a stockholder. For stock-settled SARs, the participant will have no rights as a stockholder with respect to any shares covered by the SAR until the award is exercised by the participant and we issue the shares. At the time of grant, the Compensation Committee will determine such matters as: (a) the number of shares subject to the award; (b) whether the award will be settled in cash, shares, or a combination of both; (c) the exercise price,

which may not be less than 100% of the fair market value of a share on the grant date; (d) the vesting schedule; and (e) the term of the SAR. A SAR may be granted independently or in combination with a related stock option. The term of an SAR may not exceed 10 years from the grant date.

Restricted Stock and Restricted Stock Units. A restricted stock award is an award to the participant of shares of our stock, which may be subject to restrictions on sale or transfer and/or recoverable by us if specified conditions are not met. A restricted stock unit is an award entitling the participant to receive shares or the cash equivalent of shares at a future date, subject to restrictions. In either case, the lapse of these restrictions may be based on continuing employment (or other business relationship) with us and our subsidiaries and/or achievement of performance goals. At the time of grant, the Compensation Committee will determine such matters as: (a) the number of shares subject to the award; (b) the purchase price or consideration (if any) for the shares; (c) the restrictions placed on the shares; (d) the date(s) when the restrictions placed on the shares will lapse or the performance period during which the achievement of the performance goals will be measured; and (e) in the case of restricted stock units, whether the award will be paid in shares or the cash equivalent of the value of shares. During the period that the restrictions are in place, a participant granted restricted stock will have the rights of a stockholder, including voting and dividend rights, but not the right to sell or transfer the shares, and subject to the obligation to return the share under specified circumstances. A participant granted restricted stock units does not have stockholder rights until shares are issued, if at all.

Qualified Performance-Based Awards. Any of the awards under the 2010 Plan may be granted as qualified performance-based awards under Section 162(m) of the Code. As determined by the Compensation Committee, the performance goals applicable to an award may be based upon one or more of the following performance criteria: revenue; gross profit or margin; operating profit or margin; earnings before or after interest, taxes, depreciation, and/or amortization; net earnings or net income (before or after taxes); earnings per share; share price (including, but not limited to, growth measures and total stockholder return); cost reduction or savings; return measures (including, but not limited to, return on assets, capital, invested capital, equity, sales or revenue); cash flow (including, but not limited to, operating cash flow, free cash flow, cash flow return on equity and cash flow return on investment); productivity ratios or other metrics; performance against budget; market share; working capital targets; economic value added (net operating profit after tax minus the sum of capital multiplied by the cost of capital); financial ratio metrics; and organizational/transformation metrics. These measures may be measured against our performance or other benchmarks. The Compensation Committee may provide in any such award that any evaluation of performance may include or exclude certain specified events that occur during a performance period.

Limited Transferability of Awards. Awards generally may not be sold or transferred, other than by will or by the applicable laws of descent and distribution or pursuant to a domestic relations order entered by a court of competent jurisdiction.

Effect of Change in Control and other Corporate Transactions. In the event of (i) a Change in Control with respect to us as defined in the 2010 Plan, including certain changes in ownership or Board composition, specified mergers, or sale of all or substantially all of our assets or (ii) and other merger, consolidation, sale of substantially all of our assets or other reorganization (collectively, (i) and (ii) are referred to as “Covered Transactions” in the 2010 Plan), any outstanding awards that are not assumed by the successor or substituted with an equivalent award (or if we are the surviving company in the transaction, any awards for which the transaction does not result in a continuation of such award) will be fully vested and exercisable, including shares that would not otherwise have been vested and exercisable, and shall remain exercisable for a period of fifteen (15) days from the date of notice from the Compensation Committee to the participant of such acceleration of vesting, and the award shall terminate at the end of such period.

The 2010 Plan grants the Compensation Committee authority to provide that any award shall become fully vested and exercisable in any Covered Transaction, including in the event of a participant’s termination of service without “Cause” or for “Good Reason” (as such terms are defined in the 2010 Plan) within a designated period (not to exceed 18 months) following the effective date of any Covered Transaction. All unvested options currently outstanding under the 2010 Plan vest on involuntary termination of employment within 18 months following a Covered Transaction.

Liquidation. In the event of our proposed liquidation or dissolution, each participant will be notified as soon as practicable before the effective date of the proposed transaction. The Compensation Committee may provide

for a participant to have the right to exercise any outstanding awards until 10 days prior to the transaction (including by accelerating the exercise of awards that would not otherwise be exercisable) and may provide that repurchase options or forfeiture rights on awards can lapse if the proposed transaction takes place as contemplated. To the extent not exercised prior to the transaction, an award will terminate.

U.S. Federal Income Tax Consequences. The following is a summary of the general federal income tax consequences to participants who are U.S. taxpayers and to us relating to awards granted under the 2010 Plan. This summary is not intended to be exhaustive and does not address all matters that may be relevant to a particular participant based upon his or her specific circumstances.

Incentive Stock Options. No taxable income is recognized when an incentive stock option is granted or exercised (except for purposes of the alternative minimum tax). If the participant exercises an incentive stock option and then later sells or otherwise disposes of the shares more than two years after the grant date and more than one year after the exercise date, the difference between the sale price and the exercise price will be taxed as capital gain or loss. If the participant exercises the incentive stock option and then later sells or otherwise disposes of the shares before the end of the two- or one-year holding periods described above, he or she generally will have ordinary income at the time of the sale equal to the fair market value of the shares on the exercise date (or the sale price, if less) minus the exercise price of the option. Any additional gain or loss will be capital gain or loss.

Nonstatutory Stock Options and Stock Appreciation Rights. No taxable income is recognized when a nonstatutory stock option or a stock appreciation right is granted to a participant. Upon exercise, the participant will recognize ordinary income in an amount equal to the excess of the fair market value of the shares on the exercise date over the exercise price. Any additional gain or loss recognized upon later disposition of any shares received on exercise is capital gain or loss.

Restricted Stock. The federal income tax consequences of restricted stock depend on the facts and circumstances of each award, including, in particular, the nature of any restrictions imposed with respect to the awards. In general, unless the participant makes a valid election under Section 83(b) of the Code to be taxed at the time of grant of restricted stock, if an award is subject to a “substantial risk of forfeiture” (e.g., conditioned upon the future performance of substantial services by the participant) and is nontransferable, the participant will not have taxable income upon the grant of restricted stock. Instead, at the time the participant holds stock or other property free of any substantial risk of forfeiture or transferability restrictions, the participant will recognize ordinary income equal to the fair market value (on that date) of the shares or other property less any amount paid. Alternatively, the participant may elect under Section 83(b) of the Code to include as ordinary income in the year of grant of restricted stock, an amount equal to the fair market value (on the grant date) of the restricted stock less any amount paid.

Restricted Stock Units. In general, the participant will not have taxable income upon the grant of restricted stock units. Instead, when the restricted stock units vest and the participant receives stock or other property pursuant to the restricted stock units, the participant will recognize ordinary income equal to the fair market value (on the date of receipt) of the shares or other property less any amount paid.

Tax Withholding. Ordinary income recognized on exercise of nonstatutory stock options and stock appreciation rights, on vesting of restricted stock and restricted stock and on delivery of stock or other property under units is subject to income tax and employment tax withholding, unless the participant is a non-employee director or consultant. The Compensation Committee may allow a participant to satisfy his or her tax withholding requirements under federal and state tax laws in connection with the exercise or receipt of an award by electing to have shares withheld, and/or by delivering to us already-owned shares of our common stock.

Tax Effect for Us. We generally will be entitled to a tax deduction for an award under the 2010 Plan in an amount equal to the ordinary income realized by a participant at the time the participant recognizes the income (for example, the exercise of a nonstatutory stock option). However, Section 162(m) of the Code limits our ability to deduct the annual compensation to the principal executive officer and the next three most highly compensated officers (other than the principal financial officer) to $1,000,000 per individual, unless the qualified performance-based compensation requirements of Section 162(m) are met.

This summary does not contain all information about the 2010 Plan. The complete text of the 2010 Plan as amended to date can be found by reading the original 2010 Plan, which can be found in Annex A to our

definitive proxy statement for our 2010 Annual Meeting of Stockholders filed with the SEC on April 28, 2010, together with the 2014 Amendment to the 2010 Plan, which can be found in Annex C to our definitive proxy statement for our 2015 Annual Meeting of Stockholders filed with the SEC on April 28, 2015. A copy of the 2016 Amendment to the 2010 Plan is included as Annex C to this Proxy Statement. The foregoing description of the 2010 Plan is qualified in its entirety by reference to the full text of the 2010 Plan, the 2014 Amendment and the 2016 Amendment, which are incorporated herein by reference.

Other Information

Because all awards made under the 2010 Plan, as amended, will be made at the Compensation Committee’s discretion, the benefits and amounts that will be received or allocated under the 2010 Plan and the 2014 Amendment are not determinable at this time. The closing price of the common stock, as reported on NASDAQ on April 19, 2016, was $95.02 per share.

Vote Required

The affirmative vote of the holders of a majority of the shares of our common stock present at the Annual Meeting in person or by proxy and entitled to vote on this proposal will be required to approve the 2016 Amendment to the Stamps.com 2010 Equity Incentive Plan. Abstentions will be counted towards the tabulation of votes cast and will have the same effect as negative votes, whereas broker non-votes, if any, will not be counted for purposes of determining whether the proposal has been approved.

Recommendation of our Board

Our Board recommends that the stockholders vote “FOR” approval of the 2016 Amendment to the Stamps.com 2010 Equity Incentive Plan.

PROPOSAL FOUR: RATIFICATION OF INDEPENDENT AUDITORS

Pre-Approval Policy

MANAGEMENT

The following table sets forth certain information regarding our executive officers as of April 15, 2016:

EXECUTIVE COMPENSATION

The Committee did not ultimately make any similar discretionary upward adjustment to the 2015 non-equity incentive plan (the “2015 Plan”) amounts that were earned in fiscal 2015 and are to be paid in 2016. On April 9, 2015, the Committee had approved both the 2015 Plan and a special one-time deal bonus related to the completion and announcement of the intended acquisition of Endicia for certain of our executives and other key employees in the aggregate amount of $280,000 (the “Endicia Deal Bonus”). The Endicia Deal Bonus was a special one-time bonus separate from the 2015 Plan intended to recognize the extraordinary effort of our executive management in the completion of the definitive agreement to acquire Endicia. However, upon the recommendation of our chief executive officer, the Committee determined in April 2016 that the $280,000 Endicia Deal Bonus would be deemed included within the 2015 Plan amounts (even though $20,000 of the Endicia Deal Bonus was not paid to the executive officers), such that the amount to be paid out in May 2016 would be reduced by the $280,000 previously paid.

Overall Methodology of Setting Compensation

On April 15, 2016,March 28, 2018, the Compensation Committee approved the final incentive compensation for 2015,2017, established the base salaries for 2016,2018, and established an incentive compensation plan for 20162018 (all decisions collectively, the “2016“2018 Compensation Decisions”). In doing so, the Compensation Committee and the chief executive officer utilized reports and data from Equilar, Inc. (“Equilar”), a company that provides standardized data based on U.S. proxy data from all publicly traded companies. Equilar.

For 2016, each corporate officer’s base salary was set by the Compensation Committee between the 3825^th and 6682^thnd percentile versus the 20162018 Equilar Benchmarks. In particular, the salaries for our chief executive officer and our chief financial officer and co-president, for 20162018 were set at approximately the 5268^ndth percentile versus their respective 2016 Equilar Benchmarks. In addition, the salaries for our co-president and corporate and business development officer, chief product & strategy officer and chief legal officer were set at the 6625^th, 38^th and 51^st percentiles, respectively, versus the 20162018 Equilar Benchmarks.

The 2018 salary for our chief technology officer was set pursuant to our hiring negotiations with him. The chief executive officers of our ShipStation and ShippingEasy subsidiaries were not executive officers at the time 2018 salaries were set. Accordingly, their 2018 base salaries were established through evaluation and comparison to Culpepper data for employees in similar positions, which is the same method we generally use for all our non-executive officers.

and/ and / or non-cash items such as ASC 718-related expenses, litigation charges, non-recurring adjustments, changes in the ShipStation earn-outnon-cash contingent consideration valuation, corporate development / acquisition expenses, and other one-time and non-recurring items). The Compensation Committee set the amount of the 20152018 Base Pool at $1,800,000,$4.1 million so that, if executive management performedperforms at a reasonable level and is able to generate results at the midpoint of the guidance range, as a group they would receive a total cash compensation for 2015 slightly above2018 at the median level (at the 7174^stth percentile) versus the 2015 Equilar Benchmarks. If the executive management were to achieve performance that would resultof those companies in the 2015 bonus pool being set at the $1.8 million level, the 2015 Plan would represent approximately 42% of the total fiscal 2015 compensation for the executive managers eligible for bonuses under the 2015 Plan.

2018 Equilar Benchmark.

Based on these factors and an assessment that each of the named executive officers had satisfied his or her individual goals and objectives, the Compensation Committee set the individual allocation of the 20152018 bonus pool as well as 2018 discretionary and/or contractual bonuses for executives compensated outside of the 2018 bonus pool. The compensation was as follows:

Committee further proposed a 3%30% decrease be applied to the 20162019 Base Pool if the company achieves performance at the low end of its guidance range and the resulting equivalent non-GAAP adjusted EBITDA.range. The Committee further proposed a 33%30% increase be applied to the 20162019 Base Pool if the company achieves performance at the high end of its guidance range and the resulting equivalent non-GAAP adjusted EBITDA.range. To illustrate some possible outcomes of the 20162019 Plan, the following table (i) shows the potential aggregate pool resulting under the 20162019 Plan if the company achieves a financial outcome at the top end, midpoint, and bottom end of our guidance range and (ii) compares the resulting executive management team total cash compensation to the total cash compensation of the 20162019 Equilar benchmarks:

In general, income recognized by employees upon the exercise of nonqualified stock options is tax-deductible fortax deductible by us, subject to any limitations that may be imposed by Section 162(m). Gain with respect to such options that are granted or modified after November 2, 2017. Income recognized by an employee with respect to an incentive stock option will not be tax deductible by us unless there is a “disqualifying disposition” of the shares by the employee. A disqualifying disposition occurs when an employee sells or disposes of incentive stock option shares within two years after the grant date or within one year after the exercise date. TheUpon a disqualifying disposition, the employee is taxed on a portion of the gain, based on stock value at the time of exercise of the incentive stock option, at ordinary income tax rates. rates, and such portion of the gain may be tax deductible by us.

COMPENSATION COMMITTEE REPORT

GRANTS OF PLAN-BASED AWARDS

OUTSTANDING EQUITY AWARDS AT FISCAL YEAR-END