Microsoft Defender for Office 365 vs MailGuard Comparison: Everything You Need to Know Before Choosing

Microsoft Defender for Office 365 protects the whole of Office 365 against advanced threats, extending the baseline filtering included with Exchange Online into a layered defence against the attacks that ordinary spam filtering does not catch. The distinction matters because the threats that actually breach organisations are rarely mass-market spam. They are targeted, well-written messages that reference real colleagues and real projects, carry no malware at all, and ask the recipient to approve a payment, re-enter credentials or open a document on a convincing but fraudulent site. Defender for Office 365 is built around detecting that class of attack. Safe Attachments opens incoming files in an isolated sandbox and observes their behaviour before delivery, catching malicious documents too new to appear in any signature database. Safe Links rewrites URLs and re-checks them at the moment a user clicks, which defeats the common technique of sending a clean link and weaponising the destination hours later, and applies across Outlook, Teams, Word, Excel and PowerPoint. Anti-phishing policies use machine learning and mailbox intelligence to model each user's normal correspondents and flag impersonation of executives, colleagues and trusted domains — the mechanism behind business email compromise. Protection extends beyond mail to SharePoint, OneDrive and Teams, where files are scanned and malicious content blocked, closing a route that mail-only filtering leaves open. For security teams, Threat Explorer and real-time detections allow investigation across the tenant, automated investigation and response performs triage and remediation without manual work, and campaign views group related messages so an entire attack is understood rather than individual reports. Attack simulation training runs realistic phishing exercises against staff and assigns targeted training to those who fall for them. Integration with the wider Microsoft Defender suite correlates email signals with endpoint and identity telemetry. Licensing is delivered through Microsoft 365 plans; pricing, trial and free-version details are not populated in this listing.