The best email security for small business starts with the protection already built into Microsoft 365 and Google Workspace, then adds a specialist tool if phishing and fake invoices still get through. Microsoft Defender for Office 365 suits most Microsoft customers, while API-based tools such as Abnormal Security and IRONSCALES catch business email compromise that has no malicious link or attachment. This guide compares seven options and explains how to choose between built-in and add-on protection.
Key takeaways
- Email is the most common way attacks start, through phishing, malware and fake payment requests.
- Turn on and tune the built-in protection first; many businesses never do.
- Gateway tools filter mail before it arrives; API tools scan inside the mailbox and catch impersonation.
- Set up SPF, DKIM and DMARC so criminals cannot easily spoof your domain.
- Pair any tool with a rule that payment changes are confirmed by phone.
Which is the best email security for small business? Quick picks
The options below work with Microsoft 365, Google Workspace or both. They differ in how they connect (gateway or API), what they detect best and how much management they need.
| Tool | Best for | Platforms / type | Free option |
|---|---|---|---|
| Microsoft Defender for Office 365 | Microsoft 365 customers | Microsoft 365 | Plan 1 included in Business Premium |
| Google Workspace built-in protection | Google Workspace customers | Google Workspace | Included |
| Abnormal Security | Catching business email compromise | Microsoft 365, Google Workspace (API) | No |
| IRONSCALES | Small teams that want phishing reporting and training together | Microsoft 365, Google Workspace (API) | Free trial |
| Proofpoint Essentials | Classic gateway filtering for small businesses | Microsoft 365, Google Workspace, other mail | No |
| Mimecast | Filtering plus archiving and continuity | Microsoft 365, Google Workspace | No |
| Check Point Harmony Email | Inline API protection for email and collaboration apps | Microsoft 365, Google Workspace, Slack, Teams | Free trial |
How we chose: We compared each product on support for Microsoft 365 and Google Workspace, detection of phishing and business email compromise, deployment method, ease of management for small teams and independent reviews. Features and plans change often, so confirm current pricing on each vendor’s site before you buy. We do not accept payment for placement in this list.
Why is email security so important?
Most cyberattacks on small businesses start with an email: a fake login page, a malicious attachment or a request to change bank details. Business email compromise is especially costly because the messages often contain no malware at all, only a convincing request from a spoofed or hijacked account. The FBI’s IC3 consistently reports it among the most expensive types of cybercrime.
Gateway or API: what is the difference?
- Secure email gateways sit in front of your mailbox. You change your MX records so mail passes through them first.
- API-based tools connect directly to Microsoft 365 or Google Workspace and scan messages inside the mailbox, including internal email. They are faster to deploy and better at spotting impersonation.
Many small businesses now use built-in protection plus an API-based tool rather than a gateway.
The best email security for small business options reviewed
1. Microsoft Defender for Office 365: best for microsoft 365 customers
Defender for Office 365 adds Safe Links, Safe Attachments and anti-impersonation protection on top of Exchange Online’s built-in filtering. Plan 1 is included in Microsoft 365 Business Premium, making it the first upgrade to consider. Our guide to securing Microsoft 365 covers setup.
- Strengths: Native integration, no mail routing changes, good value in Business Premium.
- Watch out for: Needs tuning; impersonation policies are not on by default.
Official site: microsoft.com
2. Google Workspace built-in protection: best for google Workspace customers
Gmail blocks the vast majority of spam and phishing, and Workspace admins can enable extra protections against suspicious attachments, spoofing and external sender warnings. Our Google Workspace security checklist lists the settings.
- Strengths: Strong default filtering, included in every plan, easy admin settings.
- Watch out for: Fewer controls than specialist tools for targeted impersonation.
Official site: workspace.google.com
3. Abnormal Security: best for catching business email compromise
Abnormal connects through the email platform’s API and uses behavioural AI to learn normal communication patterns, flagging unusual requests such as invoice changes from a vendor’s compromised account.
- Strengths: Strong at impersonation and vendor fraud, no mail routing changes, quick deployment.
- Watch out for: Aimed at mid-size and larger businesses; pricing may be high for very small teams.
Official site: abnormal.ai
4. IRONSCALES: best for small teams that want phishing reporting and training together
IRONSCALES combines AI-based phishing detection with crowd-sourced reporting from users and built-in simulation training. It is popular with managed service providers and smaller companies.
- Strengths: API-based, includes training and simulations, user reporting button.
- Watch out for: Best features on higher plans; tuning may be needed.
Official site: ironscales.com
5. Proofpoint Essentials: best for classic gateway filtering for small businesses
Proofpoint Essentials brings the market-leading gateway to smaller businesses, with spam and malware filtering, link protection, encryption and continuity options.
- Strengths: Proven filtering, email encryption and continuity options.
- Watch out for: Gateway setup needs MX record changes; interface feels dated to some users.
Official site: proofpoint.com
6. Mimecast: best for filtering plus archiving and continuity
Mimecast offers email security with archiving and continuity, so mail keeps flowing if your provider has an outage. It suits businesses that need retention for compliance.
- Strengths: Archiving and continuity, strong filtering, wide feature set.
- Watch out for: More complex to manage; usually priced for larger small businesses and above.
Official site: mimecast.com
7. Check Point Harmony Email: best for inline API protection for email and collaboration apps
Harmony Email and Collaboration (formerly Avanan) scans email and collaboration apps through APIs and can block threats before they reach the inbox. It also covers files shared in Teams, Slack and cloud drives.
- Strengths: Covers collaboration apps too, inline API protection, broad threat detection.
- Watch out for: Feature-rich console can be more than a very small team needs.
Official site: checkpoint.com
What else protects your email?
- Set up SPF, DKIM and DMARC; see DMARC, SPF and DKIM explained.
- Require MFA on every mailbox, ideally phishing-resistant.
- Mark external emails with a warning banner.
- Disable automatic forwarding to outside addresses.
- Train staff, and add a report-phishing button.
- Confirm any payment or bank detail change by phone using a known number.
Related reading
Best Free Cybersecurity Tools for Small Businesses
Frequently asked questions
Is Microsoft 365 email security enough on its own?
Exchange Online Protection blocks most spam and malware, but targeted phishing and impersonation can slip through. Defender for Office 365 or an API-based tool adds much stronger protection.
Does Google Workspace need extra email security?
Gmail’s filtering is strong, so many small businesses are well protected with the right settings. Add a specialist tool if you face frequent impersonation or invoice fraud.
What is the best tool against business email compromise?
Behavioural, API-based tools such as Abnormal Security and IRONSCALES are designed to catch impersonation without malicious links. A phone-verification rule for payments is equally important.
Do I need to change my MX records?
Only for gateway products such as Proofpoint Essentials and Mimecast. API-based tools connect without changing mail routing.
How much does email security cost?
Most charge per mailbox per month. Defender for Office 365 Plan 1 is included in Microsoft 365 Business Premium, which is often the most cost-effective start.
Our verdict
Start by turning on everything included in your plan: Defender for Office 365 for Microsoft customers, or Gmail’s advanced settings for Google Workspace. If phishing and invoice fraud still get through, add an API-based tool such as IRONSCALES or Abnormal. Then lock down your domain with DMARC and take our free Cybersecurity Readiness Assessment.
Sources and further reading
Official vendor websites and public guidance referenced in this guide. Plans and features change, so confirm details with each vendor. Last reviewed: November 2026.
- FBI’s IC3 (ic3.gov)
- microsoft.com (microsoft.com)
- workspace.google.com (workspace.google.com)
- abnormal.ai (abnormal.ai)
- ironscales.com (ironscales.com)
- proofpoint.com (proofpoint.com)
- mimecast.com (mimecast.com)
- checkpoint.com (checkpoint.com)
