Who is the CISO of Mimecast?

Leslie Nielsen is the current Chief Information Security Officer of Mimecast on CISO Tribune's record, appointed in the week of September 1, 2025.

How many security-leadership moves has CISO Tribune tracked at Mimecast?

CISO Tribune has tracked 1 move at Mimecast since September 1, 2025.

When was Leslie Nielsen appointed at Mimecast?

Leslie Nielsen's appointment as Chief Information Security Officer of Mimecast was announced in the week of September 1, 2025, per SecurityWeek Industry Moves (week of 2025-09-01).

Where did Leslie Nielsen work before becoming Chief Information Security Officer of Mimecast?

The record of the appointment gives Leslie Nielsen's previous role as SVP and CISO at Klaviyo.

What does Mimecast sell?

Mimecast sells Managed Threat Response. Managed Threat Response: 24x7 analyst response to every user-reported email.

Who does Mimecast fit?

From its own pages, Mimecast sells mainly to organizations that want to reduce risk caused by human actions across email, chat and file-sharing. Its pages say its plans are designed for businesses of all sizes, and its customer stories cover both small and medium businesses and enterprises. Mimecast says Incydr offers FedRAMP-authorized solutions suited to government agencies and contractors. It describes Cloud Archive as helping IT, Legal, Compliance and HR teams respond to legal inquiries or compliance audits. Its pages also point to security teams that handle user-reported email and insider risk.

How does CISO Tribune file Mimecast?

CISO Tribune files Mimecast under Email security, with Email authentication and DMARC, Collaboration app security and Insider risk management as secondary categories.

Where is Mimecast headquartered?

Mimecast is headquartered in London, United Kingdom.

Mimecast is owned by Permira, which acquired it in 2022.

Company record · security vendor

Mimecast CISO: Leslie Nielsen

CISO Tribune company record: Mimecast, seat filled, since week of September 1, 2025

The current Chief Information Security Officer of Mimecast, as tracked by CISO Tribune, is Leslie Nielsen, whose appointment was announced in the week of September 1, 2025 (SecurityWeek Industry Moves (week of 2025-09-01)). Previously SVP and CISO at Klaviyo. Read the record. The record entered the Wire on September 26, 2026.

Career profile: Leslie Nielsen on CISO Spotlights ↗

Tracked by the Wire since September 1, 2025 · 1 recorded move · every claim links to a sourced record · Updated November 10, 2026

Where Mimecast appears on the record (43)

Every page on CISO Tribune and its network that carries this company, 43 in all.

On the Wire: Leslie Nielsen named Chief Information Security Officer at Mimecast · 2025-09-01
Career profile: Leslie Nielsen on CISO Spotlights ↗
Compared with (37): vs Abnormal AI, vs Adaptive Security, vs Archipelo, vs Barracuda Networks, vs Broadcom, vs Check Point Software Technologies, vs Code42, vs Cofense, vs Cyberhaven, vs Cynet, vs Darktrace, vs DigiCert, vs dmarcian, vs Doppel, vs DTEX Systems, vs EasyDMARC, vs Egress, vs Guardz, vs Gurucul, vs Hilt, vs Hornetsecurity, vs IRONSCALES, vs Jazz, vs Judy Security, vs KnowBe4, vs Material Security, vs Next DLP, vs NINJIO, vs Proofpoint, vs Red Sift, vs Sendmarc, vs Sublime Security, vs Teramind, vs Trend Micro, vs Trustifi, vs Valimail, vs Virtru
In the vendor directory (4): Email security vendors · primary category
Email authentication and DMARC vendors · category
Collaboration app security vendors · category
Insider risk management vendors · category

About Mimecast

CISO Tribune's Leadership Bench files Mimecast under Cybersecurity Vendors and North America. The Wire has one security-leadership move at Mimecast on record, announced in the week of September 1, 2025.

Security leadership timeline

2025-09-01

Leslie Nielsen named Chief Information Security Officer at Mimecast

Leslie Nielsen has joined Mimecast as Chief Information Security Officer, coming from Klaviyo where he served as SVP and CISO.

What Leslie Nielsen has said in public

CISO Tribune's Voices section carries 7 public posts and talks by Leslie Nielsen. The most recent are listed with their dates.

On employee behavior as a factor in security incidents, LinkedIn, November 6, 2026.
On CISO priorities for incident disclosure versus click metrics, LinkedIn, November 5, 2026.
On lessons learned from serving as CISO across multiple companies, LinkedIn, November 4, 2026.
On workplace policies at previous companies, LinkedIn, October 23, 2026.
On risk-based security program strategy, LinkedIn, October 22, 2026.

Leslie Nielsen's record

Security chiefs at other Cybersecurity Vendors organizations

Other organizations CISO Tribune files under Cybersecurity Vendors with a named security chief on record: those in North America first, in alphabetical order from Mimecast onward.

Noma Security: Diana Kelley, Chief Information Security Officer (CISO).
Onspring: Nichole Windholz, Chief Information Security Officer (CISO).
RAD Security: Raj Umadas, Chief Information Security Officer (CISO).
RegScale: Dale Hoak, Chief Information Security Officer.
Rubrik: Michael Mestrovich, Chief Information Security Officer.
Sectigo: Jason Scott, Chief Information Security Officer.
Semperis: John Podboy, Chief Information Security Officer.
Socure: Mark Carter, Chief Information Security Officer.

The full Cybersecurity Vendors bench

What the company sells

Mimecast describes the problem it addresses as human risk. Its solutions page says Mimecast offers a unified and dynamic solution to rapidly identify and reduce risk caused by human actions and to empower users to make smarter security decisions. Mimecast says a unified platform with integrated protection across email, chat and file-sharing is essential to safeguard an organization's collaboration.

For email and collaboration threat protection, Mimecast says its solution blocks phishing, BEC, impersonation, malware and collaboration-based attacks using adaptive AI across email, Teams, Slack and more.

Mimecast Managed Threat Response is a managed service for emails that users report. Mimecast says each report is analyst-investigated, classified and remediated 24x7. Mimecast says the service works with the existing report button and that API outputs route to a SIEM, SOAR or case management platform.

For insider risk, Mimecast Incydr is the data protection product. Mimecast says Incydr brings email, endpoint, cloud, browser and agentic risk surfaces into one view, scored for risk and tied back to people. Mimecast says Incydr offers adaptive controls that range from in-the-moment education to allow-with-justification to targeted blocking. The Agent Risk Center, part of Mimecast Incydr, discovers the agents operating in an environment, classifies their AI activity against the customer's rules, and applies controls to reduce data exposure. Mimecast says Incydr offers data residency options and FedRAMP-authorized solutions, and that an ultra-lightweight agent supports Windows, Mac and Linux.

For security behavior management, Mimecast Engage delivers behavior-driven interventions powered by the Human Risk Command Center. Mimecast says Engage can deliver nudges via email, Slack or Teams, and that it offers 200+ training modules available in 27 languages. Mimecast says Engage connects with security tools such as CrowdStrike, Okta and Netskope.

For archiving, Mimecast Cloud Archive provides self-service tools to collect, discover, preserve and review collaboration data. Mimecast says Supervision supports review, escalation, export and reporting, Sync & Recover protects files, folders, contacts, tasks and notes, and Archive for MS Teams keeps encrypted copies of Teams data.

Mimecast says it protects and supports 42,000+ organizations globally and has done so since 2003. Its pages say it offers 300+ integrations.^{[2][5][7][9][10][11][15][16][17][18]}

Categories: Email security (primary category)
Email authentication and DMARC
Collaboration app security
Insider risk management
Compare Mimecast with companies in the same category
Headquarters: London, United Kingdom^[1]
Founded: 2003^[1][6]
Ownership: Owned by Permira since 2022^{[3][4][8][13][14][19]}
CISO on record: Leslie Nielsen, Chief Information Security Officer (appointment announced in the week of September 1, 2025)
Website: mimecast.com

Products and services

Product names as the company writes them; what each does, in our words, from the company's own product pages. Never how well it does it.

Managed Threat Response^[8]
24x7 analyst response to every user-reported email.
Mimecast Managed Threat Response has analysts investigate, classify and remediate each email users report. It works with the existing report button.

Competitors and alternatives

The other companies on our record filed under the same categories, category by category: first those that lead with that category and share more of Mimecast's categories, then alphabetical. A list from the record, never a ranking.

On email security, Mimecast competes with Proofpoint, Hornetsecurity, Trustifi, Abnormal AI, Barracuda Networks, Cofense, Egress, IRONSCALES, Material Security, Sublime Security and 12 more.
On email authentication and dmarc, Mimecast competes with dmarcian, EasyDMARC, Red Sift, Sendmarc, Valimail, Hornetsecurity and DigiCert.
On collaboration app security, Mimecast competes with Proofpoint, Trustifi and Virtru.
On insider risk management, Mimecast competes with Code42, DTEX Systems, Teramind, Proofpoint, Archipelo, Cyberhaven, Gurucul, Hilt, Jazz and Next DLP.

What review platforms show

The headline rating and review count each platform showed in public search results on the day we looked, with the link. We do not read or reproduce the reviews, and a rating is the platform's, not ours.

G2 · 4.5 out of 5^[13]seen November 4, 2026
Gartner Peer Insights · 4.7 out of 5^[19]seen November 4, 2026

References

Every fact above cites one of these by number. Tier A is the company itself, a regulator or a filing; tier B is trade or business press.

[1]CompanyMimecast · mimecast.com · undated page, accessed September 27, 2026 · Tier A: the company, a regulator or a filing
[2]ProductsMimecast · mimecast.com · undated page, accessed September 27, 2026 · Tier A: the company, a regulator or a filing
[3]Permira completes acquisition of mimecastPermira · permira.com · published May 17, 2022 · Tier A: the company, a regulator or a filing
[4]Human Risk Management & Advanced Email Security | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[5]Advanced Email Security | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[6]Mimecast Incydr | See & Stop Data Loss From Insiders | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[7]Security Awareness Training | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[8]Email Incident Response Service | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[9]Email Archive | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[10]Aware | Keep Collaboration Secure & Compliant | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[11]Cybersecurity Products and Services | MimecastMimecast · undated page, accessed October 26, 2026 · Tier A: the company, a regulator or a filing
[12]Mimecast Appoints Ranjan Singh as Chief Executive OfficerGlobeNewswire · published June 25, 2026 · Tier A: the company, a regulator or a filing
[13]Mimecast Advanced Email Security Reviews & Product Details - G2G2 · undated page, accessed October 26, 2026 · Tier C
[14]Mimecast Reviews, Ratings & Features 2026 | Gartner Peer InsightsGartner Peer Insights · undated page, accessed October 26, 2026 · Tier C
[15]Cyber Security Solutions | MimecastMimecast · undated page, accessed November 4, 2026 · Tier A: the company, a regulator or a filing
[16]Email & Collaboration Threat Protection | MimecastMimecast · undated page, accessed November 4, 2026 · Tier A: the company, a regulator or a filing
[17]Collaboration Threat Protection | MimecastMimecast · undated page, accessed November 4, 2026 · Tier A: the company, a regulator or a filing
[18]Mimecast Plans | MimecastMimecast · undated page, accessed November 4, 2026 · Tier A: the company, a regulator or a filing
[19]Mimecast Reviews, Ratings & Features 2026 | Gartner Peer InsightsGartner Peer Insights · undated page, accessed November 4, 2026 · Tier C

Last verified September 27, 2026. Our code found the quoted passage behind each fact on its source page when the fact was recorded, and re-checks every record against its sources each month.

Recorded September 27, 2026, expanded November 4, 2026 from the references above.

Work for Mimecast? Suggest a correction to a fact on this page (with a source on your own domain), or claim this entry by publishing a small file on your domain.

Questions CISOs ask about Mimecast

Who is the CISO of Mimecast?: Leslie Nielsen is the current Chief Information Security Officer of Mimecast on CISO Tribune's record, appointed in the week of September 1, 2025.
How many security-leadership moves has CISO Tribune tracked at Mimecast?: CISO Tribune has tracked 1 move at Mimecast since September 1, 2025.
When was Leslie Nielsen appointed at Mimecast?: Leslie Nielsen's appointment as Chief Information Security Officer of Mimecast was announced in the week of September 1, 2025, per SecurityWeek Industry Moves (week of 2025-09-01).
Where did Leslie Nielsen work before becoming Chief Information Security Officer of Mimecast?: The record of the appointment gives Leslie Nielsen's previous role as SVP and CISO at Klaviyo.
Who are the security chiefs at other Cybersecurity Vendors organizations?: On CISO Tribune's record they include Diana Kelley at Noma Security, Nichole Windholz at Onspring, Raj Umadas at RAD Security and Dale Hoak at RegScale.
Has Leslie Nielsen spoken or written publicly?: CISO Tribune's Voices section carries 7 public posts and talks by Leslie Nielsen, the most recent dated November 6, 2026.
What does Mimecast sell?: Mimecast sells Managed Threat Response. Managed Threat Response: 24x7 analyst response to every user-reported email.
Who does Mimecast fit?: From its own pages, Mimecast sells mainly to organizations that want to reduce risk caused by human actions across email, chat and file-sharing. Its pages say its plans are designed for businesses of all sizes, and its customer stories cover both small and medium businesses and enterprises. Mimecast says Incydr offers FedRAMP-authorized solutions suited to government agencies and contractors. It describes Cloud Archive as helping IT, Legal, Compliance and HR teams respond to legal inquiries or compliance audits. Its pages also point to security teams that handle user-reported email and insider risk.
How does CISO Tribune file Mimecast?: CISO Tribune files Mimecast under Email security, with Email authentication and DMARC, Collaboration app security and Insider risk management as secondary categories.
Where is Mimecast headquartered?: Mimecast is headquartered in London, United Kingdom.
When was Mimecast founded?: Mimecast was founded in 2003.
Who owns Mimecast?: Mimecast is owned by Permira, which acquired it in 2022.

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