Microsoft 365 email security combines Microsoft Defender for Office 365, encryption, data loss prevention, and Secure Score monitoring to block phishing, malware, and data leaks. You strengthen it by enabling the built-in protections and tuning the advanced policies your business actually needs.
Last updated: May 28, 2026
Email is one of the most widely used communication tools for businesses of every size. It’s also one of the most common attack vectors for cybercriminals who want to compromise your data, devices, and reputation. Phishing remains the dominant way attackers steal credentials, and the scale is hard to ignore. Microsoft tracks more than 600 million identity attacks every day, and over 99% of them are password-based, according to its 2024 Digital Defense Report. To protect your organization, you need layered email security that can prevent, detect, and respond to attacks. Microsoft 365 gives you the features to do that, but only if you configure them properly. A well-planned cybersecurity strategy ties these settings together instead of leaving them as scattered defaults.
This article walks through the tips and best practices that actually move the needle on your Microsoft 365 email security.
Enable and Use the Built-in Protection Features of Microsoft Defender for Office 365
Microsoft Defender for Office 365 is a cloud-based service that protects email from attacks such as credential phishing, business email compromise, and ransomware. It uses machine learning, a large database of threat signals, and other heuristics to identify and block malicious messages, attachments, and links. Here’s how the four built-in protections compare.
| Protection | What it does | What it blocks |
|---|---|---|
| Safe Attachments | Detonates email attachments in a sandbox before they reach the inbox | Malware and ransomware payloads |
| Safe Links | Rewrites and re-checks URLs at the moment you click them | Phishing and malicious links |
| Anti-phishing | Uses machine learning and impersonation detection | Credential theft, spoofing, domain impersonation |
| Anti-spam | Filters unsolicited and bulk mail | Spam, mass phishing, email harvesting |
Safe Attachments
This feature scans every email attachment for malware before it reaches your inbox, and it also protects files in SharePoint Online, OneDrive, and Teams. You can build custom policies that decide how to handle suspicious attachments, whether that means blocking, replacing, or redirecting them.
Safe Links
This feature checks links in email and other Microsoft 365 apps for malicious or phishing content, then re-checks each link at the moment you click it to confirm it’s still safe. You can create custom policies that block, warn, or allow suspicious links. Microsoft explains the full mechanism in its Safe Links overview.
Anti-phishing
This feature uses machine learning and impersonation detection to catch phishing messages that try to trick you into handing over credentials, personal information, or financial details. It also defends against spoofing and domain impersonation. Your custom policies decide what happens next, from moving messages to junk, to deleting them, to adding a warning banner.
Anti-spam
This feature filters out unwanted and unsolicited messages that may carry spam, malware, or phishing content, and it shields you from bulk email and email-harvesting attacks. You can set policies that route spam to junk, delete it, or flag it with a warning banner.
Enhance Your Email Security with Advanced Configuration and Customization Options
Beyond the built-in protections, Microsoft Defender for Office 365 gives you advanced configuration options that let you tailor email security to your business. These include the following.
Encryption
Encryption lets you protect email messages and attachments with a digital certificate or a password. It ensures that only the intended recipients can read your content and prevents unauthorized access or tampering. It also helps you meet requirements under regulations like GDPR and HIPAA.
Data Loss Prevention (DLP)
DLP stops the accidental or intentional leak of sensitive data such as credit card numbers, Social Security numbers, or health records. It’s a core tool for meeting compliance standards like GDPR and HIPAA. Microsoft’s Purview DLP documentation breaks down how the policies work across Microsoft 365.
Transport Rules
Transport rules let you create and apply custom rules that control how email flows based on conditions and actions you set. You can use them to enforce your own security policies, such as requiring encryption, blocking attachments, or preventing auto-forwarding.
Mail Flow Rules
Mail flow rules control how messages are routed based on conditions and actions. You can route specific messages to different recipients, servers, or domains, or modify message properties like the subject, the sender, or the priority.
Features of Microsoft Defender for Office 365
Defender for Office 365 doesn’t just block threats. It also helps you detect, investigate, respond to, and hunt them. These are the features you’ll rely on most.
Alerts
Alerts notify you of suspicious or malicious activity in your email environment, from malware infections to phishing campaigns to data breaches. You can also create custom alerts based on your own criteria, such as sender, recipient, subject, or attachment.
Automated Investigation and Response (AIR)
AIR triggers investigations that help you remediate and contain threats. It uses automation and artificial intelligence to analyze alerts, collect evidence, find the root cause, and apply the right action, whether that’s deleting, quarantining, or blocking malicious messages, attachments, or links.
Threat Analytics
Threat Analytics gives you detailed, actionable intelligence from Microsoft security researchers. You can use it to understand the nature and scope of active threats and apply the recommendations that fit your organization.
Threat Explorer
Threat Explorer helps you identify risks, evaluate mail flow patterns, spot trends, and assess the effect of changes you make during tuning. You can also remove messages from your organization with a few clicks.
Monitor and Improve Your Email Security Posture with Microsoft 365 Secure Score and Other Tools
Microsoft 365 Secure Score measures and improves your security posture across Microsoft 365, including email. It rates your settings and actions, compares them with industry benchmarks and best practices, and gives you prioritized recommendations to raise your score. Working through those actions is one of the fastest ways to close real gaps, as Microsoft details in its Secure Score guide.
Alongside Secure Score, two more tools help you monitor and improve email security.
Message Trace
Message Trace lets you track and troubleshoot email delivery. You can find the status, recipients, senders, subject, size, and date of a message, identify any errors during delivery, and export the results to a CSV file for analysis or reporting.
Mail Flow Insights
Mail Flow Insights gives you dashboards and reports on the health and performance of your email environment. You can monitor message volume, latency, delivery, and bounce rates, then spot trends or anomalies that affect email quality and reliability.
Microsoft 365 Email Security Questions, Answered
What is Microsoft 365 email security?
It’s the set of built-in tools that protect Microsoft 365 mailboxes from phishing, malware, and data loss. Core layers include Microsoft Defender for Office 365, anti-spam and anti-phishing filters, encryption, and data loss prevention policies.
Is Microsoft Defender for Office 365 included in my plan?
Defender for Office 365 comes in Plan 1 and Plan 2. Plan 2 is included with Microsoft 365 E5, while other plans add it as a paid upgrade. Check your license before you assume Safe Links and Safe Attachments are already active.
How are Safe Links and Safe Attachments different?
Safe Attachments detonates email attachments in a sandbox to catch malware before delivery. Safe Links rewrites and re-checks URLs at click time, so a link that turns malicious after delivery still gets blocked.
Does Microsoft 365 encrypt email automatically?
Not by default for every message. You enable message encryption and apply transport or mail flow rules so sensitive email is encrypted automatically, which also supports compliance with standards like HIPAA and GDPR.
How does Microsoft 365 Secure Score help?
Secure Score rates your current security settings, benchmarks them against best practices, and lists prioritized actions. Working through those recommendations is the fastest way to close gaps in your email security posture.
Conclusion
Email security is one of the hardest and most important parts of your overall posture in Microsoft 365. By following the practices in this article, you can turn on the right built-in protections, fine-tune your advanced configuration, use Defender’s detection and response tools to contain threats faster, and track your progress with Secure Score. If you’d rather not manage it alone, our managed IT services team handles it end to end.
Want your Microsoft 365 email locked down without the guesswork?
Uprite configures Defender for Office 365, encryption, and DLP policies for businesses that can’t afford a breach, then monitors Secure Score so your protection keeps improving. Get a free email security assessment and see exactly where your gaps are.
Or call us at (866) 570-3065.
