Rafeal E. Brown - 19 May 2022 Form 4 Insider Report for Mimecast Ltd

Footnote F1

Pursuant to the terms of that certain Transaction Agreement between Magnesium Bidco Limited ("Magnesium Bidco") and Mimecast Limited ("Issuer"), dated December 7, 2021 (the "Transaction Agreement"), Magnesium Bidco agreed to acquire all of the issued and to be issued ordinary shares of Issuer for $80.00 per ordinary share by means of a court-sanctioned scheme of arrangement (the "Scheme"). At the effective time of the Scheme on May 19, 2022 (the "Effective Time"), each ordinary share then outstanding was automatically transferred from Issuer's shareholders to Magnesium Bidco in accordance with the Scheme and the Transaction Agreement, and Issuer's shareholders ceased to have any rights with respect to the Issuer ordinary shares, except their rights under the Scheme, including their right to receive $80.00 per ordinary share, subject to required withholding taxes.

Footnote F2

In connection with the Effective Time of the court-sanctioned scheme of arrangement contemplated by the Transaction Agreement and the election by the Reporting Person to participate in the equity of Permira or its affiliates following the Effective Time, the Reporting Person exchanged the legal and beneficial ownership of each ordinary share of Issuer held by the Reporting Person for shares of Magnesium Topco Limited, an affiliate of Permira, prior to the Effective Time.

Footnote F3

Each restricted share unit ("RSU") represents a contingent right to receive one Issuer ordinary share.

Footnote F4

At the Effective Time, each RSU that was vested and outstanding as of immediately prior to the Effective Time ("Vested RSU") was canceled and converted into the right to receive an amount in cash equal to $80.00 multiplied by the aggregate number of shares subject to such Vested RSU, subject to required withholding taxes. Each RSU that was outstanding as of immediately prior to the Effective Time and that was not a Vested RSU ("Unvested RSU") was converted into and substituted with a cash award in an amount equal to $80.00 multiplied by the aggregate number of shares underlying such Unvested RSU immediately prior to the Effective Time, in each case subject to the same time-vesting terms and conditions that applied to the substituted Unvested RSU as in effect immediately prior to the Effective Time, including the requirement of continued service with Magnesium Bidco or its affiliates through the applicable vesting date.

Footnote F5

These RSUs were granted on April 1, 2019. 25% of the shares vested on April 1, 2020 and the remainder of the shares vest on an annual basis over the next 3 years.

Footnote F6

These RSUs were granted on April 1, 2020. 25% of the shares vested on April 1, 2021 and the remainder of the shares vest on an annual basis over the next 3 years.

Footnote F7

These RSUs were granted on April 1, 2021. 25% of the shares vested on April 1, 2022 and the remainder of the shares vest on an annual basis over the next 3 years.

Footnote F8

Each option to purchase Issuer ordinary shares ("Option") that was vested and outstanding, and unexercised as of immediately prior to the Effective Time ("Vested Option") was canceled and extinguished and converted into the right to receive an amount in cash equal to (x) the difference, if any, between $80.00 and the per-share exercise price of such Vested Option, multiplied by (y) the aggregate number of shares underlying such Vested Option, subject to required withholding taxes. Each Option that was outstanding as of immediately prior to the Effective Time and that was not a Vested Option ("Unvested Option") was automatically converted into and substituted with a cash award in an amount equal to (x) the difference, if any,

Footnote F9

(Continued from Footnote 8) between $80.00 and the per-share exercise price of such Unvested Option, multiplied by (y) the aggregate number of shares underlying such Unvested Option, in each case subject to the same time-vesting terms and conditions that applied to the substituted Unvested Option as in effect immediately prior to the Effective Time, including the requirement of continued service with Magnesium Bidco or its affiliates through the applicable vesting date.

Footnote F10

This Option was granted on April 1, 2019. 25% of the shares vested on April 1, 2020 and the remainder of the shares vest on a quarterly basis over the next 3 years.

Footnote F11

This Option was granted on April 1, 2020. 25% of the shares vested on April 1, 2021 and the remainder of the shares vest on a quarterly basis over the next 3 years.

Footnote F12

This Option was granted on April 1, 2021. 25% of the shares vested on April 1, 2022 and the remainder of the shares vest on a quarterly basis over the next 3 years.