You Have Microsoft 365. Is Your Email Actually Protected?

If your organization uses Microsoft 365, you've likely already started leveraging the native email security features. But is this enough? Will adding another product improve your security, or will the cost of more complexity in your environment outweigh the benefits?

I don't pose this as an academic question. These are real conversations we have with customers whose decisions are shaped by budget, team size, technical knowledge and the risks they are trying to address.

The stakes can be substantial. According to the FBI’s 2025 Internet Crime Report, the agency received 24,768 complaints involving business email compromise (BEC), with reported losses exceeding $3 billion.

Closer to home, I have seen what can happen when an organization relies on little more than the protections accompanying a basic Microsoft 365 mailbox. In some situations, it's an ongoing battle against compromised email, internal phishing and compromised accounts being used to target customers and partners. An IT team can end up chasing one incident after another without the right technology or adequate visibility into the problem to get ahead of it. It's inefficient, it's painful, and it can create the wrong impression on the organizations and people whose trust it depends upon.

That does not mean Microsoft’s security is ineffective any more than it means that every organization should purchase a third-party product. What I'm here to suggest is that we need to be precise, and about what “Microsoft security” includes, what risks the organization faces and what its IT team can realistically manage.

Start by Understanding What You Already Have

“Microsoft email security” is often discussed as though it were one product. In practice, the phrase can describe several materially different levels of protection.

Exchange Online includes baseline protections such as anti-spam, anti-malware, anti-spoofing, quarantine and related administrative controls. Microsoft says its built-in anti-malware protection for Exchange Online also scans internal messages, along with inbound and outbound mail. These protections are real, and it would be inaccurate to describe a standard Microsoft mailbox as having no security at all, assuming these baseline protections are enabled and correctly configured.

But baseline protection should not be mistaken for a complete email-security program. In environments experiencing persistent phishing, impersonation, account compromise or BEC (Business Email Compromise), I have found the baseline inadequate for reliable risk prevention and problem resolution.

The next level is Microsoft Defender for Office 365 Plan 1. It adds capabilities such as Safe Links, Safe Attachments, enhanced anti-phishing protection and real-time detections. Plan 1 is included with Microsoft 365 Business Premium, Microsoft 365 E3, or available as a stand-alone add on.

Defender for Office 365 Plan 2 goes even further, adding more advanced investigation and response capabilities such as Threat Explorer, automated investigation and response, advanced hunting and attack simulation training. It is included with Microsoft 365 E5 and is also available through Microsoft’s Defender Suite for Business Premium.

These distinctions matter. Comparing a 3^rd party email solution such as Mimecast to the default protection included with an Exchange Online mailbox is not the same as comparing it to a fully licensed and configured Microsoft Defender environment.

Before buying anything, an organization should determine which Microsoft licenses it owns, which protections those licenses provide and, equally important, which capabilities have actually been configured.

The Microsoft Decision Is Also a Bundle Decision

One of Microsoft’s greatest strengths is also what makes the purchasing decision complicated: Microsoft does not sell email security in isolation.

Microsoft 365 Business Premium includes Defender for Office 365 Plan 1, but that is only one component. The package also includes Defender for Business endpoint protection, Intune Plan 1 for device and application management, Entra ID Plan 1, and Microsoft Purview information-protection and data-loss-prevention capabilities.

For an organization that intends to use those services, the bundle can deliver considerable value. Email, identity, endpoints, devices and data can be managed as parts of a more integrated security environment.

But a bundle is economical only when the organization will use and operate enough of it to receive that value.

Suppose the immediate requirement is narrowly focused on improving email security. Perhaps the organization is dealing with phishing, BEC, impersonation or employees repeatedly clicking malicious links. Purchasing a broader Microsoft license may provide many additional capabilities, but those capabilities have limited practical value if the organization does not need them or lacks the resources to deploy them.

In that situation, a focused email-security product may be the more appropriate investment.

This is why a simple price comparison does not tell the whole story. Organizations should compare the total value they expect to consume, not merely the number of features included in each license.

When a Purpose-Built Platform May Be the Better Fit

When email represents a particular pain point or opportunity, we commonly lead with a purpose-built email-security platform from a vendor such as Mimecast or Proofpoint.

The reasoning is not that Microsoft cannot provide serious email security. It is that vendors focused on email security concentrate their development, threat intelligence, workflows and support around a narrower set of problems.

Both Mimecast and Proofpoint, for example, offer email protection through secure email gateways and API-based deployments. Their offerings emphasize threats such as phishing, BEC, impersonation, malicious links, account takeover and post-delivery remediation.

The right deployment model depends on what the organization needs. A secure email gateway can provide granular pre-delivery filtering and routing control. An API-based product can integrate with a cloud email environment without requiring the same mail-routing changes.

A purpose-built platform can also provide capabilities that are less about identifying one additional malicious message and more about changing the architecture around email.

Continuity is a good example. Mimecast offers a separate continuity service designed to keep email available when the primary email system is down. For an organization that considers email essential to its operations, independence from its primary provider may be a legitimate business-resilience requirement.

Purpose-built platforms can also be attractive in mixed environments involving Microsoft 365, Google Workspace, hybrid systems or on-premises infrastructure. Some combine email protection with focused security-awareness programs, behavioral risk information, targeted training or email-specific administrative support.

None of this proves that a purpose-built platform will always detect more threats or deliver better results. It does show why an organization with a specific email-security problem might prefer a platform built around that problem.

More Security Products Do Not Automatically Mean More Security

If one layer of security is good, turning on two or three might sound even better. Operationally, it does not always work that way.

In email environments, multiple filtering systems can delay delivery. Administrators may have to maintain whitelists, exclusions and policies in more than one platform. When a legitimate message is blocked, it may be unclear which product stopped it or where it must be released.

Overlapping tools also increase costs beyond their subscription prices. Every additional console and policy requires employee time. Someone must configure the product, review alerts, investigate problems, maintain exceptions and ensure that updates in one system do not conflict with another.

Microsoft’s own guidance illustrates this coordination problem. During migrations between third-party email security and Defender for Office 365, Microsoft recommends carefully controlling which platform performs which filtering functions. Its documentation specifically notes that double wrapping of links is unsupported when a third-party service and Microsoft Safe Links are both attempting to rewrite URLs.

The opposite problem can be even more dangerous. Instead of two tools performing the same function, each platform may be configured under the assumption that the other is providing a particular protection. The organization believes it has overlapping coverage when the control is actually disabled on both sides.

These gaps are difficult to see when the IT team is already spread thin. Frequently, they are discovered only during an incident—when it is too late to prevent the damage.

Regular configuration audits should therefore be part of the decision from the beginning. Security tools are not “set it and forget it” products. Licenses change, features are introduced, exceptions accumulate and responsibilities shift. The environment you designed two years ago may not be the environment you are operating today.

Defense in depth requires coordinated layers, not merely additional layers

Seven Questions to Ask Before Choosing

Rather than beginning with vendors, I recommend working through seven questions.

1. What problem are we trying to solve?

“Improve email security” is too broad. Are you concerned about BEC, malicious links, domain impersonation, compromised accounts, downtime, data loss or another specific exposure?

A clearly defined problem gives you something against which products and outcomes can be evaluated.

2. What protection do we currently have?

Determine whether the organization is using baseline Exchange protection, Defender for Office 365 Plan 1, Plan 2 or another product. Do not make a purchasing decision based only on the Microsoft 365 name shown on an invoice.

3. Is the existing protection configured correctly?

An organization may own the appropriate technology while receiving little benefit from it because policies were never enabled, tuned or reviewed. A configuration problem should not automatically become a product purchase.

4. Will we use the broader Microsoft bundle?

If the organization will also use Intune, Defender for Business, Entra ID, extended detection and response (XDR), and Purview, Microsoft’s integrated approach may be compelling. If email is the only immediate requirement, a specialized email-security platform may provide a more focused path.

5. Who will operate and manage the solution?

Licensing a capability does not ensure that alerts will be investigated, policies maintained or reports reviewed. Consider the size and experience of the internal team, along with the support available from the vendor or a technology partner.

6. What complexity will another platform introduce?

Before adding a product, map how messages, links and attachments will be inspected. Decide which system owns each policy, where quarantined messages will appear and who will maintain routing, exclusions and connectors.

7. How will we know whether it worked?

Define success before implementation. Measures might include reductions in successful phishing, BEC attempts reaching users, false positives, delivery delays, incident-response time, administrative labor or downtime exposure.

Without agreed-upon outcomes, it is difficult to know whether the additional investment has reduced risk or merely added technology.

Choose the Architecture You Can Actually Operate

Microsoft’s security stack can provide substantial value, particularly when an organization intends to use its broader identity, endpoint, device-management and data-protection capabilities.

A purpose-built platform may be the better choice when email is the defined pain point, independent continuity matters, the environment extends beyond Microsoft, or focused workflows and expertise justify the investment.

Both approaches can work. Both can also fail when protections are left at their defaults, products are poorly coordinated or no one is responsible for operating them.

The best email-security platform is not necessarily the one with the most capabilities. It is the one that addresses the organization’s actual risks without creating an environment its team cannot effectively manage.

If you are uncertain about the protections included in your Microsoft environment—or whether optimizing what you own or adding a specialized email-security platform is the better next step—Prescriptive can help assess the current configuration, identify gaps and design an email-security strategy around your organization’s real needs.