Exhibit 99.1

Mimecast Announces Fourth Quarter and Full Year 2021 Financial Results

Lexington, MA – May 11, 2021 (GLOBE NEWSWIRE) Mimecast Limited (NASDAQ: MIME), a leading global provider of next generation cloud security and risk management services for email and corporate information, today announced financial results for the fourth fiscal quarter and fiscal year ended March 31, 2021.

Fourth Quarter 2021 Highlights

Peter Bauer, chief executive officer of Mimecast, said, “We delivered solid results against what remains a challenging macro backdrop, which speaks to the durability of our business model, our differentiated platform, and our focused execution against our three-pronged strategy. We are staying close to our customers, continuing to strengthen our go-to-market teams and strategies, and innovating on and expanding our platform to anticipate the evolving threat landscape.”

Mr. Bauer continued, “Our targeted strategic growth initiatives are beginning to take hold. We believe that with continued focused execution, as economies in our markets rebound, we will reaccelerate top-line growth over time. At the same time, we continue to drive increasingly strong free cash flow and meaningful margin expansion.”

Fourth Quarter 2021 Financial and Operating Highlights

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Full Year 2021 Financial and Operating Highlights

Reconciliations of the non-GAAP financial measures provided in this press release to their most directly comparable GAAP financial measures are provided in the financial tables included at the end of this press release. An explanation of these measures and how they are calculated is also included under the heading “Non-GAAP Financial Measures.”

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Financial Outlook

Mimecast is providing guidance for the first quarter 2022 and fiscal year 2022.  Our guidance is based on exchange rates as of May 3, 2021.

First Quarter 2022 Guidance:

Fiscal Year 2022 Guidance:

GAAP net income (loss) is the most comparable GAAP measure to Adjusted EBITDA. Adjusted EBITDA differs from GAAP net income (loss) in that it excludes depreciation, amortization, disposals and impairment of long-lived assets, acquisition-related gains and expenses, litigation-related expenses, share-based compensation expense, restructuring expense, interest income and interest expense, the benefit from (provision for) income taxes and foreign exchange (expense) income. Mimecast is unable to predict with reasonable certainty the ultimate outcome of these exclusions without unreasonable effort. Therefore, Mimecast has not provided guidance for GAAP net income (loss) or a reconciliation of forward-looking Adjusted EBITDA guidance to GAAP net income (loss). The reconciliation between net cash provided by operating activities to guided free cash flow for the first quarter 2022 and fiscal year 2022 is provided in the financial tables included at the end of this press release.

The financial guidance provided above includes forward-looking statements within the meaning of U.S. securities laws. While the financial guidance considers the anticipated impact of the Company’s recent security incident and the global COVID-19 pandemic, the future effect of the security incident and the pandemic on Mimecast’s financial results is highly uncertain. Mimecast’s actual results may differ materially. See “Safe Harbor for Forward-Looking Statements” below.

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Conference Call and Webcast Information

Mimecast will host a conference call to discuss these financial results for investors and analysts at 8:00 am EDT (UTC-05:00) on May 11, 2021. To access the conference call, dial (844) 293-0173 for the U.S. and Canada and +1 (661) 378-9976 for international callers, conference ID# 3694729. The call will also be webcast live on the investor relations section of the Company’s website https://investors.mimecast.com.  An audio replay of the call will be available two hours after the live call ends by dialing (855) 859-2056 for U.S. and Canada or +1 (404) 537-3406 for international callers, conference ID# 3694729.  An archive of the webcast will be available on the investor relations section of the Company’s website https://investors.mimecast.com.

Mimecast: Relentless protection. Resilient world.™

Mimecast (NASDAQ: MIME) was born in 2003 with a focus on delivering relentless protection. Each day, we take on cyber disruption for our tens of thousands of customers around the globe; always putting them first, and never giving up on tackling their biggest security challenges together. We are the company that built an intentional and scalable design ideology that solves the number one cyberattack vector – email. We continuously invest to thoughtfully integrate brand protection, security awareness training, web security, compliance and other essential capabilities. Mimecast is here to help protect large and small organizations from malicious activity, human error and technology failure; and to lead the movement toward building a more resilient world. www.mimecast.com

Mimecast and the Mimecast logo are registered trademarks of Mimecast. All other third-party trademarks and logos contained in this press release are the property of their respective owners.

Non-GAAP Financial Measures

We have provided in this press release financial information that has not been prepared in accordance with GAAP. We use these non-GAAP financial measures internally in analyzing our financial results and believe they are useful to investors, as a supplement to GAAP measures, in evaluating our ongoing operational performance. We believe that the use of these non-GAAP financial measures provides an additional tool for investors to use in evaluating ongoing operating results and trends and in comparing our financial results with other companies in our industry, many of which present similar non-GAAP financial measures to investors.

Non-GAAP financial measures should not be considered in isolation from, or as a substitute for, financial information prepared in accordance with GAAP. Investors are encouraged to review the reconciliation of these non-GAAP financial measures to their most directly comparable GAAP financial measures provided in the financial statement tables included below in this press release.

Revenue Constant Currency Growth Rate. We believe revenue constant currency growth rate is a key indicator of our operating results. We calculate revenue constant currency growth rate by translating revenue from entities reporting in foreign currencies into U.S. dollars using the comparable foreign currency exchange rates from the prior fiscal period. To determine projected revenue growth rates on a constant currency basis for the first quarter and full year 2022, expected revenue from entities reporting in foreign currencies is translated into U.S. dollars using the comparable prior year period’s monthly average foreign currency exchange rates.

Non-GAAP gross profit and Non-GAAP gross profit percentage. We define non-GAAP gross profit as gross profit, adjusted to exclude: share-based compensation expense and amortization of acquired intangible assets. We define non-GAAP gross profit percentage as non-GAAP gross profit divided by GAAP revenue. We consider these non-GAAP financial measures to be useful metrics for management and investors because they exclude the effect of non-cash charges for share-based compensation expense and amortization of acquired intangible assets so that our management and investors can compare our recurring core business net results over multiple periods. There are a number of limitations related to the use of non-GAAP gross profit and non-GAAP gross profit percentage versus gross profit and gross profit percentage calculated in accordance with GAAP. For example, as noted above, non-GAAP gross profit and gross profit percentage excludes share-based compensation expense and amortization of acquired intangible assets. Management compensates for these limitations by providing specific information regarding the GAAP amounts excluded from non-GAAP gross profit and non-GAAP gross profit percentage and evaluates non-GAAP gross profit and non-GAAP gross profit percentage together with gross profit and gross profit percentage calculated in accordance with GAAP.

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Non-GAAP operating expenses and Non-GAAP income from operations. We provide investors with certain non-GAAP financial measures, including non-GAAP research and development expense, non-GAAP sales and marketing expense, non-GAAP general and administrative expense and non-GAAP income from operations (collectively the “non-GAAP operating financial measures”). These non-GAAP operating financial measures exclude the following, as applicable (as reflected in the reconciliation tables that follow):  share-based compensation expense; amortization of acquired intangible assets; impairment of long-lived assets; restructuring expense; acquisition-related gains and expenses; and litigation-related expenses. We consider these non-GAAP operating financial measures to be useful metrics for management and investors because it excludes the effect of share-based compensation expense and certain “one-time” charges so that our management and investors can compare our recurring core business net results over multiple periods. There are a number of limitations related to the use of these non-GAAP operating financial measures versus the applicable financial measures calculated in accordance with GAAP. For example, as noted above, the non-GAAP operating financial measures exclude share-based compensation expense and certain “one-time” charges. In addition, the components of the costs that we exclude in our calculation of non-GAAP operating financial measures may differ from the components that our peer companies exclude when they report their non-GAAP results of operations. Management compensates for these limitations by providing specific information regarding the GAAP amounts excluded from non-GAAP operating financial measures and evaluates non-GAAP operating financial measures together with the applicable financial measures calculated in accordance with GAAP.

Non-GAAP net income. We define non-GAAP net income as net income (loss), adjusted to exclude: share-based compensation expense; amortization of acquired intangible assets; impairment of long-lived assets; restructuring expense; acquisition-related gains and expenses; litigation-related expenses; and the income tax effect of non-GAAP adjustments. We consider this non-GAAP financial measure to be a useful metric for management and investors because it excludes the effect of share-based compensation expense, certain “one-time” charges and related income tax effects so that our management and investors can compare our recurring core business net results over multiple periods. There are a number of limitations related to the use of non-GAAP net income versus net income (loss) calculated in accordance with GAAP. For example, as noted above, non-GAAP net income excludes share-based compensation expense, certain “one-time” charges and related income tax effects. In addition, the components of the costs that we exclude in our calculation of non-GAAP net income may differ from the components that our peer companies exclude when they report their non-GAAP results of operations. Management compensates for these limitations by providing specific information regarding the GAAP amounts excluded from non-GAAP net income and evaluating non-GAAP net income together with net income (loss) calculated in accordance with GAAP.

Adjusted EBITDA and Adjusted EBITDA margin. We believe that Adjusted EBITDA and Adjusted EBITDA margin are key indicators of our operating results. We define Adjusted EBITDA as net income (loss), adjusted to exclude: depreciation; amortization; disposals and impairment of long-lived assets; acquisition-related gains and expenses; litigation-related expenses; share-based compensation expense; restructuring expense; interest income and interest expense; the benefit from (provision for) income taxes; and foreign exchange (expense) income. We define Adjusted EBITDA margin as Adjusted EBITDA over GAAP revenue in the period. We use Adjusted EBITDA as part of our overall assessment of our performance, for planning purposes, including the preparation of our annual operating budget, to evaluate the effectiveness of our business strategies, to communicate with our board of directors concerning our financial performance and for establishing incentive compensation metrics for executives and other senior employees.

Free cash flow. We define free cash flow as net cash provided by operating activities minus capital expenditures. We consider free cash flow to be a liquidity measure that provides useful information to management and investors about the amount of cash generated by the business that, after the acquisition of property, equipment and capitalized software, can be used for strategic opportunities, including investing in our business, and strengthening the balance sheet. Analysis of free cash flow facilitates management’s comparisons of our operating results to competitors’ operating results. A limitation of using free cash flow versus the GAAP measure of net cash provided by operating activities as a means for evaluating our company is that free cash flow does not represent the total increase or decrease in the cash balance from operations for the period because it excludes cash used for capital expenditures during the period. Management compensates for this limitation by providing information about our capital expenditures on the face of the cash flow statement and in the liquidity and capital resources discussion included in our annual and quarterly reports filed with the Securities and Exchange Commission.

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Safe Harbor for Forward-Looking Statements

Statements in this press release regarding management’s future expectations, beliefs, intentions, goals, strategies, plans or prospects, including, without limitation, the Company’s recent security incident, including the scope and impact of the attack, the number and location of impacted customers, and the effectiveness of any current or future isolation and remediation efforts, the impact of the global COVID-19 pandemic on Mimecast’s operations and financial performance, the impact of foreign exchange rates, the durability of Mimecast’s business model, Mimecast’s differentiated platform, management’s ability to execute, the potential to reaccelerate top line revenue growth, the likelihood of economic recovery, Mimecast’s strategic growth initiatives, product innovation and expansion, Mimecast’s investments in its go-to-market team, expanding cash flow, margin expansion, and Mimecast’s future financial performance on both a GAAP and non-GAAP basis under the heading “Financial Outlook” above, may constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 and other federal securities laws. All statements, other than statements of historical fact, are statements that could be deemed forward-looking statements, including statements containing the words “predicts,” “plan,” “expects,” “anticipates,” “believes,” “goal,” “target,” “estimate,” “potential,” “may,” “might,” “could,” “see,” “seek,” “forecast,” and similar words. Mimecast intends all such forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 21E of the Securities Exchange Act of 1934, as amended, and the Private Securities Litigation Reform Act of 1995. Such forward-looking statements involve known and unknown risks, uncertainties and other factors including, but not limited to, uncertainties and risks relating to the recent security incident, the reputational, financial, legal and other risks related to potential adverse impacts to our customers and partners as a result of the security incident, the impact of the global COVID-19 pandemic on the Company’s business, operations, employees and financial results, the ability to attract new customers and retain existing customers, particularly during challenging economic times, competitive conditions, data breaches related to the recent security incident or otherwise, compliance with data privacy and data transfer laws and regulations related to the recent security incident or otherwise, service disruptions, the effect of the withdrawal of the United Kingdom from the European Union, risks associated with failure to protect the Company’s intellectual property or claims that the Company infringes the intellectual property of others, the successful integration of the Company’s acquisitions, including DMARC Analyzer B.V., Segasec Labs Limited and MessageControl and other acquisitions the Company may complete, the global nature of the Company’s business, including foreign currency exchange rate fluctuations and the potential disparate economic impact of the global COVID-19 pandemic on the jurisdictions in which the Company operates, and the other risks, uncertainties and factors detailed in Mimecast’s filings with the Securities and Exchange Commission. As a result of such risks, uncertainties and factors, Mimecast’s actual results may differ materially from any future results, performance or achievements discussed in or implied by the forward-looking statements contained herein. Mimecast is providing the information in this press release as of this date and assumes no obligations to update the information included in this press release or revise any forward-looking statements, whether as a result of new information, future events or otherwise.

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MIMECAST LIMITED

CONSOLIDATED STATEMENTS OF OPERATIONS

(in thousands, except per share amounts)

(unaudited)

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MIMECAST LIMITED

CONSOLIDATED BALANCE SHEETS

(in thousands, except share and per share amounts)

(unaudited)

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MIMECAST LIMITED

CONSOLIDATED STATEMENTS OF CASH FLOWS

(in thousands)

(unaudited)

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Key Performance Indicators

In addition to traditional financial metrics, such as revenue and revenue growth trends, we monitor several other non-GAAP financial measures and non-financial metrics to help us evaluate growth trends, establish budgets, measure the effectiveness of our sales and marketing efforts and assess operational efficiencies. The key performance indicators that we monitor are as follows:

Reconciliation of Non-GAAP Financial Measures

The following table presents a reconciliation of revenue growth rate, as reported, to revenue constant currency growth rate:

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The following tables present a reconciliation of selected GAAP results to Non-GAAP results (dollars in thousands):

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The following table presents a reconciliation of Net income (loss) to Non-GAAP net income (in thousands, except per share amounts):

The following table presents a reconciliation of Net income (loss) to Adjusted EBITDA (in thousands):

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The following table presents a reconciliation of Net cash provided by operating activities to Free cash flow (in thousands):

Share-based compensation expense for the three and twelve months ended March 31, 2021 and 2020 (in thousands):

Amortization of acquired intangible assets for the three and twelve months ended March 31, 2021 and 2020 (in thousands):

The following table presents a reconciliation of Net cash provided by operating activities to guided Free cash flow (in millions):

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Mimecast Social Media Resources