Microsoft 365 Security Features You Should Be Using

MFA is the single most effective control for preventing account takeover. Microsoft reports that MFA blocks 99.9% of automated attacks. Yet many businesses still haven't enabled it for all users — often because of concerns about user friction or the complexity of the rollout. Enable Security Defaults in Azure AD to enforce MFA across your entire organisation instantly, with no additional licensing required.

The mechanics of why MFA is so effective are worth understanding. Most credential attacks — password spraying, phishing, credential stuffing from data breaches — rely on stolen username and password combinations. MFA adds a second factor (typically a phone notification or authenticator app code) that the attacker does not have. Even if they have your password, they cannot log in without the second factor. This single control neutralises the vast majority of account takeover attempts.

The most common objection to MFA is user inconvenience. In practice, Microsoft Authenticator's number matching and passwordless sign-in options have made the experience seamless for most users. The initial setup takes 5–10 minutes per user, and the ongoing friction is minimal — a single tap on a phone notification. Compare that to the cost and disruption of a compromised account, and the case for MFA becomes overwhelming.

Defender for Office 365 adds advanced threat protection to Exchange Online, including Safe Links (real-time URL scanning), Safe Attachments (sandboxed attachment analysis), and Anti-Phishing policies. These features stop the majority of email-based attacks before they reach your inbox. Email remains the #1 attack vector for businesses of all sizes — over 90% of cyberattacks begin with a phishing email.

Safe Links works by rewriting every URL in incoming emails and scanning the destination in real time when the user clicks. This catches malicious links that were safe at the time of delivery but were later weaponised — a technique known as time-of-click phishing. Safe Attachments opens every attachment in a sandboxed environment before delivering it to the recipient, catching malware that evades signature-based detection.

The Anti-Phishing policies in Defender for Office 365 include impersonation protection — detecting emails that attempt to impersonate your executives, your domain, or trusted external senders. This is the technical control that catches Business Email Compromise attempts at the email gateway, before they ever reach your finance team. Combined with Attack Simulation Training, which sends realistic phishing simulations to your employees, Defender for Office 365 addresses both the technical and human dimensions of email security.

Conditional Access lets you enforce context-aware access controls — requiring MFA from untrusted locations, blocking legacy authentication protocols, and restricting access from non-compliant devices. This is the foundation of a Zero Trust security model: never trust, always verify. Instead of granting access based solely on username and password, Conditional Access evaluates the full context of every sign-in attempt.

Legacy authentication protocols are one of the most overlooked security risks in Microsoft 365 environments. Protocols like SMTP AUTH, POP3, IMAP, and basic authentication do not support MFA — meaning any account that allows legacy authentication can be compromised even if MFA is enabled. Blocking legacy authentication is one of the highest-impact security improvements you can make, and it is often the first thing a security-focused MSP will do when they take over a Microsoft 365 tenant.

Device compliance policies, enforced through Conditional Access and Microsoft Intune, ensure that only managed, up-to-date devices can access your corporate data. This prevents a compromised personal device from being used to access sensitive business information, and ensures that all devices accessing your environment meet your security baseline — current OS patches, antivirus enabled, disk encryption active.

Purview DLP policies automatically detect and protect sensitive information like credit card numbers, Social Security numbers, and health records. Prevent accidental or malicious data exfiltration via email, Teams, SharePoint, and OneDrive. Data loss prevention is particularly important for businesses subject to compliance requirements — HIPAA, PCI-DSS, GDPR — where a single data breach can result in significant regulatory fines in addition to the direct costs of the incident.

The most valuable aspect of Purview DLP is its policy tips feature, which educates users in real time when they attempt to share sensitive information. Instead of silently blocking an action and generating a support ticket, Purview shows the user a notification explaining why the action was blocked and what they should do instead. This turns DLP from a pure enforcement tool into an ongoing security awareness programme.

Purview's sensitivity labels extend data protection beyond your Microsoft 365 environment. Documents labelled as "Confidential" carry their protection with them — even when shared externally or downloaded to a personal device. This is particularly valuable for professional services firms, healthcare organisations, and any business that regularly shares sensitive documents with clients or partners.