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Top 10 Email Security Software

The email security tools businesses use to stop phishing, business email compromise and ransomware, ranked by how many customers each vendor says it serves.

Proofpoint Core Email Protection2M+ customers 2

Hornetsecurity 365 Total Protection125,000+ customers 3

Barracuda Email Protection80,000+ organizations

Quick answer

Proofpoint is the largest email security vendor, serving over 2M customers and more than half of the Fortune 100. Hornetsecurity is second with 125,000+ customers and an all-in-one Microsoft 365 bundle, and Barracuda is third with 80,000+ organizations on its Email Protection suite. For AI that catches what gateways miss, Abnormal AI is used by 30% of the Fortune 500.

How it's ranked: Customers or organizations each vendor says it serves, as published on its own website (read November 2026). Some counts are company-wide (Proofpoint, KnowBe4, Darktrace) and some are for the email product only (Barracuda), and each is the company's own claim, so treat them as a guide to scale, not an audit. Cisco publishes no customer count for its email product and is ranked last for that reason.

Proofpoint Core Email Protection

Proofpoint · AI email security for Microsoft 365 and Google Workspace

2M+ customers

The biggest name in email security.

Proofpoint says it has more than 5,000 team members serving over 2M customers worldwide, including more than half of the Fortune 100. It was founded in 2002 by Eric Hahn, the former CTO of Netscape, and is headquartered in Sunnyvale, California. Every day it detects and blocks threats across more than 2.6 billion emails and 28 million cloud accounts. Its Core Email Protection product claims to stop 99.999% of threats, including phishing, business email compromise and ransomware, and to detect 27% more novel threats than leading competing tools. It can run inline or through the Microsoft Graph API, which Proofpoint says can be deployed in 48 hours. It sandboxes attachments and URLs, adds warning banners to suspicious mail, and automates the handling of emails users report. It fits big organizations that want a long track record and deep threat data behind their email filter.

Best forLarge enterprises and regulated industries that want the most proven email defense

Skip it ifYou are a small business on a tight budget

Source: www.proofpoint.com/us/company/about

Hornetsecurity 365 Total Protection

Hornetsecurity (part of Proofpoint) · Microsoft 365 email security, backup and archiving

125,000+ customers

Best all-in-one bundle for Microsoft 365.

Hornetsecurity says it is trusted by over 125,000 customers worldwide, served through more than 12,000 partners, and that it has been operating for 15 years with a team of over 750 specialists. Its about page says it operates in more than 120 countries. The company has now joined forces with Proofpoint. Its 365 Total Protection suite comes in four plans. Plan 1 covers spam and malware filtering, automatic email encryption and signatures. Plan 2 adds AI-based advanced threat protection, audit-proof email archiving and a business continuity service. Plan 3 adds automated Microsoft 365 backup and recovery with unlimited storage, and Plan 4 adds security awareness training, permission management and DMARC reporting. Its annual cybersecurity report is based on an analysis of 72 billion emails. It suits small and mid-size Microsoft 365 users who buy through an IT partner.

Best forMicrosoft 365 shops that want email security, backup and archiving from one vendor

Skip it ifYou do not use Microsoft 365

Source: www.hornetsecurity.com/en/

Barracuda Email Protection

Barracuda Networks · AI email security with backup, archiving and training

80,000+ organizations

The broadest suite for smaller teams.

Barracuda says its Email Protection is trusted by more than 80,000 organizations worldwide. It covers mail before delivery, at delivery and continuously after, using an AI engine called Barracuda IQ that draws on 100+ global threat feeds and re-checks risk after a message lands. It connects to Microsoft 365 or Google Workspace by API with no MX record changes and is operational in minutes. Automated remediation pulls threats out of every mailbox, bulk actions work across thousands of mailboxes or tenants, and the Bailey assistant explains each detection in plain language. The suite also bundles Microsoft 365 backup, tamper-proof cloud archiving, encryption and security awareness training. More than 20,000 organizations have run its free Email Threat Scan, which takes under 5 minutes and needs no MX changes. It fits smaller IT teams and MSPs that want one vendor for most of their email needs.

Best forSmall and mid-size businesses and MSPs that want a broad suite

Skip it ifYou only want a single point tool

Source: www.barracuda.com/products/email-protection

KnowBe4 Cloud Email Security

KnowBe4 · Inbound, outbound and encryption for Microsoft 365

70,000+ organizations (company-wide)

Best for stopping human mistakes.

KnowBe4 says it is trusted by more than 70,000 organizations worldwide, a company-wide figure that includes its well-known security awareness training. The company was started in August 2010 by Stu Sjouwerman. Its Cloud Email Security for Microsoft 365 is a suite of three products. Defend blocks inbound phishing, ransomware and business email compromise with behavioral AI and self-learning threat models. Prevent watches outbound mail in real time inside Outlook and warns users about accidental sends or misdirected emails before they go. Protect adds policy-based email encryption. KnowBe4 says the suite stops up to 97% more targeted email attacks and uncovers 10x more hidden data breaches, and it works across all Microsoft 365 license levels without extra infrastructure. Its big difference is the focus on human error, with banners and prompts that teach users in the moment.

Best forTeams that already train staff with KnowBe4 and want email security alongside it

Skip it ifYou use Google Workspace rather than Microsoft 365

Source: www.knowbe4.com/about-us

Mimecast Advanced Email Security

Mimecast · Email and collaboration security platform

42,000+ organizations

A long-standing all-rounder.

Mimecast says it is trusted by over 42,000 organizations in more than 100 countries. It was founded in 2003 by Peter Bauer and Neil Murray, is headquartered in London, and has 2000+ employees across 13 offices on five continents. It has protected business communications for more than two decades. Its email and collaboration security layers on top of Microsoft 365's own controls to stop phishing, business email compromise, impersonation, malware and account takeover across email and the collaboration tools people use every day. Its Apex platform offers 350+ integrations plus API and MCP connections, so email signals can flow into the rest of a security stack. It also offers free DMARC, DKIM, SPF and BIMI record checkers. Mimecast Advanced Email Security holds a 4.5 rating on Gartner from 800+ reviews, according to its homepage.

Best forMid-size and large firms that want email security plus wide integrations

Skip it ifYou want an API-only add-on with no gateway

Source: www.mimecast.com/company/

IRONSCALES

IRONSCALES · AI and crowdsourced anti-phishing for the mailbox

18,000+ organizations

Best crowdsourced phishing defense.

IRONSCALES says it protects more than 18,000 organizations worldwide, from school districts and hospitals to global brands. It was founded in 2014 by alumni of the Israel Defense Forces' intelligence technology unit and is headquartered in Atlanta, Georgia, and Tel Aviv, Israel. It sells directly and through more than 3,500 managed service provider partners. It connects to Microsoft 365 and Google Workspace by API in minutes, with no MX record changes. Its Adaptive AI is paired with a threat intelligence community of more than 36,000 security professionals, so a phishing attack confirmed in one organization can be blocked in others' mailboxes. It also includes phishing simulation and training. IRONSCALES says it was the first email security vendor accepted into Anthropic's Cyber Verification Program.

Best forLean IT teams and MSPs that want fast, automated phishing response

Skip it ifYou need a traditional on-premises gateway

Source: ironscales.com/company/about-us

Darktrace / EMAIL

Darktrace · Behavioral AI email and collaboration security

10,000+ customers (company-wide)

Best behavioral AI approach.

Darktrace says it solves problems for 10,000+ customers, a company-wide figure across its security products. Its email product takes a different approach from most: instead of relying on known attack patterns or data pooled from other organizations, it learns how your own business communicates and flags messages that break that pattern. That lets it catch phishing, business email compromise, executive impersonation and other targeted attacks that signature-based tools miss. When an account is compromised, it can respond on its own by ending sessions, forcing a new login and restricting access across email, SaaS and cloud. Its behavioral detection also extends to Microsoft Teams, Zoom and Slack. Darktrace was named a Leader in the 2025 Gartner Magic Quadrant for Email Security and a Gartner Peer Insights Customers' Choice two years running.

Best forSecurity teams that want AI trained on their own organization

Skip it ifYou want a simple filter with little tuning

Source: www.darktrace.com/products/email

Abnormal AI

Abnormal AI · Behavioral AI email security delivered by API

5,000 organizations

Best for catching what gateways miss.

Abnormal AI says it is trusted by 5,000 organizations, including 30% of the Fortune 500. It was founded in 2018 to stop crime with AI. Its behavioral security platform models what is normal for each person and organization, then flags emails that break the pattern, which is aimed at AI-written phishing and business email compromise that look clean to traditional filters. It deploys in 60 seconds via API, with no MX record changes. Abnormal says that over the twelve months to May 31, 2026, it detected more than 1,200 attacks per 1,000 mailboxes each month that had already passed a secure email gateway. Beyond the inbox it also covers account takeover protection, identity threat protection and AI security. It fits large companies that want to add a strong behavioral layer on top of Microsoft 365 or an existing gateway.

Best forLarge enterprises on Microsoft 365 or Google Workspace that want to add to or replace a gateway

Skip it ifYou are a very small business

Source: abnormal.ai/

Libraesva Email Security

Libraesva (now LibraCyber) · Privacy-first AI email security from Europe

3,500+ customers

Best for EU data control.

Libraesva says it is trusted by 3,500+ customers and protects 5,000,000+ mailboxes and 70,000+ domains, with 13+ years of innovation behind it. It has been helping businesses secure their email since 2013 and has entities in Lecco, Italy, London and North Bend, Washington. Libraesva has combined with Cyber Guru to launch a new brand, LibraCyber. Its pitch is privacy-first email security: it can run locally or in your chosen cloud to keep messages within strict EU data standards. Its semantic AI looks at the intent behind each message instead of scanning for keywords, and it blocks malware, spoofing, phishing, business email compromise and account takeover. The suite adds an email archiver, a phishing simulator and LetsDMARC for domain protection. It works with Microsoft 365, Google Workspace and Exchange and offers a 30-day free trial.

Best forEuropean organizations that want data kept local

Skip it ifYou want a large US vendor with a big partner network

Source: www.libraesva.com/

Cisco Secure Email Threat Defense

Cisco · Cloud email security with gateway and API modes

No customer count published

Best for Cisco shops.

Cisco does not publish a customer count for Secure Email Threat Defense, so it is ranked last here on our measure, not on quality. The product modernizes email security into a single cloud platform driven by cloud-scale AI detections. It unifies inline gateway and API-based deployment in one console, so it can stop threats before they reach the mailbox and also remediate after delivery. It uses relationship graphs, not just message content, to spot business email compromise and phishing. Cisco says it has achieved FedRAMP certification for government and regulated customers and earned an SE Labs AAA rating. Pricing is per user, with 1-, 3- and 5-year terms, discounts for multiyear deals, no extra charge for scheduled billing, and 24/7 Cisco TAC support included. A free trial is available for Microsoft 365.

Best forOrganizations already invested in Cisco security and networking

Skip it ifYou want a standalone tool from an email specialist

Source: www.cisco.com/site/us/en/products/security/secure-email/index.html

Questions people ask

What is the best email security software?

Proofpoint is the largest, serving over 2M customers including more than half of the Fortune 100, and says its Core Email Protection stops 99.999% of threats. Hornetsecurity (125,000+ customers) and Barracuda (80,000+ organizations) are the next biggest.

What is the best email security for Microsoft 365?

Hornetsecurity 365 Total Protection bundles filtering, archiving, backup and DMARC for Microsoft 365. Abnormal AI, IRONSCALES and Barracuda all connect to Microsoft 365 by API with no MX record changes.

Which email security tool is best for small businesses?

Barracuda Email Protection deploys in minutes by API and bundles backup, archiving and training. IRONSCALES serves customers through more than 3,500 MSP partners.

Do I need email security if I use Microsoft 365?

Many vendors on this list are built to add to Microsoft 365's own protection. Abnormal AI says it found more than 1,200 attacks per 1,000 mailboxes each month that had already passed a secure email gateway.

How were these tools ranked?

By the number of customers or organizations each vendor publishes on its own website. These are the companies' own claims; Cisco publishes no count and is ranked last.

How we ranked

Customers or organizations each vendor says it serves, as published on its own website (read November 2026). Some counts are company-wide (Proofpoint, KnowBe4, Darktrace) and some are for the email product only (Barracuda), and each is the company's own claim, so treat them as a guide to scale, not an audit. Cisco publishes no customer count for its email product and is ranked last for that reason. Every number on this page comes from the source linked under each pick, and every photo shows the actual product. Brands can't pay to be on this list.

List source: www.proofpoint.com/us/company/about · Updated 2026-11-14