Defender for Office 365: Why Email Is Still the Primary Threat Vector and How Business Premium Addresses It

Email is still the most common attack entry point — accounting for more than 90% of initial access in cyber incidents according to Verizon's annual Data Breach Investigations Report. Exchange Online provides baseline protection via Exchange Online Protection (EOP). Business Premium adds Defender for Office 365 P1, which provides significantly more sophisticated protection.

What Exchange Online Protection covers

• Basic spam filtering
• Known malware detection in attachments
• Sender authentication checks (SPF, DKIM, DMARC)
• Basic phishing detection

What Defender for Office 365 P1 adds

• Safe Attachments — attachments are detonated in a sandboxed environment before delivery; malicious files never reach the user
• Safe Links — URLs in emails and Office documents are rewritten and checked at click time against the latest threat intelligence
• Anti-phishing (Advanced) — impersonation protection for your specific users and domains, plus mailbox intelligence to understand normal communication patterns
• Anti-phishing (Spoof) — composite authentication (DMARC, SPF, DKIM) with spoofing intelligence to block fake sender addresses
• Campaigns view — identifies coordinated phishing campaigns targeting your organisation as part of a broader attack

Configuration best practices

Out of the box, Defender for Office 365 applies Microsoft's standard protection preset. Optimyze configures the Strict protection preset for most clients — adding Safe Attachments for SharePoint, OneDrive, and Teams (where files are also scanned), and configuring anti-phishing user impersonation protection for all executives and finance staff. We review the Threat Explorer weekly for clients in high-risk sectors.