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For most businesses, the right starting point is the protection already included with their Microsoft 365 subscription—not an automatic purchase of another email-security layer. Check whether the tenant has baseline Exchange Online protection, Defender for Office 365 Plan 1, or Plan 2. Add a third-party service only when it addresses a defined security or operational gap and its expected benefit justifies the added cost, configuration work, false-positive risk, and changes to quarantine and security workflows.
What Microsoft 365 already protects
Microsoft 365 cloud mailboxes include baseline anti-malware, anti-spam, and anti-phishing protections enabled by default. Those protections are meaningful, but they are not the same as the additional capabilities in Defender for Office 365 Plans 1 and 2. See Microsoft’s overview of anti-malware protection and its Defender for Office 365 overview.
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Licensing varies by subscription and service plan. Microsoft says Defender for Office 365 Plan 1 is included with Office 365 E3 and Microsoft 365 E3 effective July 1, 2026. That inclusion does not provide Plan 2 capabilities. Check the actual service plans assigned to the tenant rather than assuming every Microsoft 365 edition includes the same protection. Microsoft’s Defender for Office 365 service description and plan matrix lists the distinctions.
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| Protection level | Capabilities described by Microsoft | What it means for the decision |
|---|---|---|
| Baseline Microsoft 365 protection | Anti-malware, anti-spam, and anti-phishing for Microsoft 365 cloud mailboxes, enabled by default. See Microsoft’s baseline protection documentation. | Establish what the tenant already has before buying an additional service. |
| Defender for Office 365 Plan 1 | Advanced email and collaboration protections, including Safe Links, Safe Attachments, and enhanced anti-phishing. See Microsoft’s Defender overview. | Assess whether these protections are already licensed and whether they meet the organization’s prevention and detection requirements. |
| Defender for Office 365 Plan 2 | Plan 1 protections plus capabilities such as investigation, threat hunting, automated response, and attack simulation training. See Microsoft’s plan matrix. | Consider whether the security team needs these investigation and response capabilities, not just additional message filtering. |
When a third-party email-security service may be worthwhile
A third-party layer can be reasonable if it fills a specific gap that the organization has identified—for example, a required capability, workflow, or integration that its current Microsoft 365 setup does not provide. Microsoft supports integrating non-Microsoft email-security services, but that guidance is not a recommendation that every organization should add one. Its guidance asks customers to weigh the security improvement against higher cost, configuration complexity, and false-positive rates. Read Microsoft’s integration guidance before deciding how a service would fit.
#1 Best Overall
- Watchguard T145 Firebox with 3 Year Basic Security Suite License (WGT145033) - The Firebox T145 delivers enterprise-grade protection for branch offices and retail sites. With a blend of 2.5Gb, 1Gb, and SFP/SFP+ ports, it supports high throughput, AI-driven malware protection, and DNS filtering for robust network defense.
- The Basic Security Suite activates core protections on your Firebox, including intrusion prevention, gateway antivirus, URL filtering, and spam blocking in WatchGuard Cloud. Upgrade to Total Security Suite to add AI-powered malware detection, cloud sandboxing, DNS filtering, and advanced correlation.
- The Basic Security Suite equips your WatchGuard Firebox with a robust set of foundational security tools. This bundle delivers intrusion prevention, gateway antivirus, URL filtering, and spam blocking, all managed through WatchGuard Cloud. It’s a cost-effective choice for organizations that need reliable, essential protection without unnecessary extras.
- Interfaces and deployment: 2.5Gb and 1Gb Ethernet with SFP or SFP+ fiber for clean aggregation and segmented backhaul at the edge.
- Performance and scale: UTM up to 710 Mbps with inspection on; flexible VPN topologies for hub and spoke or mesh designs.
- Define the gap: Identify the requirement the service is meant to address and how you will determine whether it meets it.
- Count the total operational cost: Include licensing, deployment and maintenance effort, investigation time, and the burden of handling false positives.
- Check the user and analyst experience: Decide where messages are quarantined, how users request release, and which team handles alerts and reporting.
- Confirm security-operations fit: Review how the service works with the organization’s existing SIEM and SOAR tools and response processes.
The Microsoft guidance reviewed for this comparison does not establish independent head-to-head detection rates or performance rankings for named vendors. A vendor choice therefore needs evidence specific to the organization’s requirements; the existence of another filtering layer alone is not proof of better protection.
How to decide what your business needs
- Verify the tenant’s entitlements. Check the organization’s subscription and assigned service plans. Distinguish baseline protection from Defender for Office 365 Plan 1 and Plan 2; do not infer Plan 2 features from Plan 1 licensing.
- Map requirements to available capabilities. Compare the organization’s prevention and collaboration-protection needs with Safe Links, Safe Attachments, and enhanced anti-phishing. Separately decide whether investigation, threat hunting, automated response, or attack simulation training is needed.
- Name any remaining gap. If considering a third party, state the specific capability or workflow it should improve. If no defined gap exists, the case for another layer is unproven.
- Estimate operational impact. Account for added cost, configuration and mail-flow complexity, possible false positives, quarantine handling, reporting, and security-team workload.
- Validate the intended setup in the tenant. Review mail flow, authentication signals, exception policies, simulations, alerting, user reporting, and quarantine behavior before relying on a coexistence design.
What to plan for when combining Microsoft 365 and another filter
Coexistence is not simply a matter of switching on two filters. The integration method affects message routing and which service sees the original sender and authentication information. Microsoft describes different integration approaches with different supportability considerations; its guidance says Enhanced Filtering for Connectors is fully supported for scenarios where an upstream service forwards messages into Exchange Online. Enhanced Filtering helps Microsoft 365 identify the messages’ original sources. See Microsoft’s non-Microsoft service integration guidance.
Rank #2
- Watchguard T125 Firebox with 1 Year Basic Security Suite License (WGT125031) - The Firebox T125 provides enterprise-grade protection for branch offices and remote sites. Featuring 2.5Gb and 1Gb ports, it delivers fast throughput, advanced malware detection with IntelligentAV, and SD-WAN compatibility in a compact form factor.
- The Basic Security Suite activates core protections on your Firebox, including intrusion prevention, gateway antivirus, URL filtering, and spam blocking in WatchGuard Cloud. Upgrade to Total Security Suite to add AI-powered malware detection, cloud sandboxing, DNS filtering, and advanced correlation.
- The Basic Security Suite equips your WatchGuard Firebox with a robust set of foundational security tools. This bundle delivers intrusion prevention, gateway antivirus, URL filtering, and spam blocking, all managed through WatchGuard Cloud. It’s a cost-effective choice for organizations that need reliable, essential protection without unnecessary extras.
- Interfaces and deployment: 1x 2.5Gb and 4x 1Gb Ethernet to simplify uplinks, carve out segmented zones, and keep branch wiring minimal.
- Performance and scale: UTM up to 510 Mbps with inspection on; sized for small and branch offices with room to grow VPN connectivity.
Preserve sender and authentication context
When an intermediary service handles or modifies a message, authentication signals may need attention. Microsoft describes ARC as a way to preserve authentication results across intermediary services. If an upstream provider modifies messages, review ARC and the alternative Microsoft notes of moving message modification to Defender. These are configuration choices to evaluate for the actual mail path, not universal settings that can be applied without testing. The relevant details are in Microsoft’s defense-in-depth guidance.
Review exceptions and security workflows
Microsoft’s defense-in-depth guidance calls out mail-flow rules and allow-list overrides that can bypass filtering. Review them alongside how users report suspicious messages, how analysts investigate alerts, and whether users face one clear quarantine experience or separate queues. Confirm that simulations and reporting continue to work as intended after changing routing or policies. See Microsoft’s guidance for organizations using non-Microsoft filtering with Defender.
Rank #3
- Watchguard T125 Firebox with 5 Year Basic Security Suite License (WGT125035) - The Firebox T125 provides enterprise-grade protection for branch offices and remote sites. Featuring 2.5Gb and 1Gb ports, it delivers fast throughput, advanced malware detection with IntelligentAV, and SD-WAN compatibility in a compact form factor.
- The Basic Security Suite activates core protections on your Firebox, including intrusion prevention, gateway antivirus, URL filtering, and spam blocking in WatchGuard Cloud. Upgrade to Total Security Suite to add AI-powered malware detection, cloud sandboxing, DNS filtering, and advanced correlation.
- The Basic Security Suite equips your WatchGuard Firebox with a robust set of foundational security tools. This bundle delivers intrusion prevention, gateway antivirus, URL filtering, and spam blocking, all managed through WatchGuard Cloud. It’s a cost-effective choice for organizations that need reliable, essential protection without unnecessary extras.
- Interfaces and deployment: 1x 2.5Gb and 4x 1Gb Ethernet to simplify uplinks, carve out segmented zones, and keep branch wiring minimal.
- Performance and scale: UTM up to 510 Mbps with inspection on; sized for small and branch offices with room to grow VPN connectivity.
Bottom line for the choice
Start by confirming the Microsoft 365 protections the business already owns, including whether Plan 1 or Plan 2 is assigned. Use those capabilities as the baseline for evaluating a third-party service. Add one only when a specific requirement remains unmet and the expected improvement outweighs its licensing, mail-flow, false-positive, and workflow costs. For any combined deployment, verify routing, authentication, policy exceptions, reporting, and quarantine behavior in the organization’s own tenant.
Quick Recap
Best Value
- The latest SonicWall TZ370 series, are the first desktop form factor nextgeneration firewalls (NGFW) with 10 or 5 Gigabit Ethernet interfaces. The series consist of a wide range of products to suit a variety of use cases.
- Reduce complexity and get the business running without relying on IT personnel with easy onboarding using SonicExpress App and Zero-Touch Deployment, and easy management through a single pane of glass
- Drive business growth by investing in next-gen appliances with multi-gigabit and advanced security features, to future-proof against the changing network and security landscape.
- SonicWall 24x7 support provides chat, email, web, and telephone support for technical assistance | Dynamic Support is designed for customers who need continued protection through ongoing firmware updates and advanced technical support
- Hardware: Operating system: SonicOS 7.0 | Interfaces: 8x1GbE, 2 USB 3.0, 1 Console | Management: Network Security Manager, CLI, SSH, Web UI, GMS, REST APIs | VLAN Interfaces: 128 | Access points supported (maximum): 16
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