Sentaro vs Microsoft Defender for Office 365: keep Defender, add Sentaro

Microsoft sells email protection as a ladder: built-in protection for every cloud mailbox (long known as Exchange Online Protection, EOP), then Defender for Office 365 Plan 1, then Plan 2. On 17 June 2026 Microsoft began rolling Plan 1 out to Microsoft 365 E3/G3 and Office 365 E3/G3; its licensing update says the features are complete by 1 August 2026, and the Defender blog says “by Fall 2026”.

Suite prices are from Microsoft’s “2026 M365 Packaging & Pricing Updates” (dated 16 February 2026), with Teams, effective 1 July 2026; plan prices are from Microsoft’s Defender for Office 365 page. All checked 18 October 2026. Your agreement price may differ.

Microsoft documents Defender’s strengths in the mail flow: reputation, spam and malware filtering, Safe Links, Safe Attachments and impersonation checks. Those controls judge a sender and a payload. Three risks sit mostly outside that documented scope.

• Fraud with no payload. A typical case: a supplier’s real mailbox is compromised and the attacker replies inside a genuine invoice thread with new bank details. There is no link or file, and the sender passes SPF, DKIM and DMARC. Sentaro’s Message vector reads intent and relationship context, such as reply-chain reuse, injected replies and suppliers that suddenly change banking details.
• Apps users connect themselves. OAuth app governance and shadow IT discovery are not part of Defender for Office 365; Microsoft sells them in Defender for Cloud Apps. Sentaro’s App vector inventories every app, AI tool and OAuth grant with scope-level risk per user, blocks consent phishing in mail flow and revokes risky grants, in every plan.
• The people to run it. Plan 2’s Threat Explorer, hunting and automated investigation assume a security team. Sentaro’s verdicts are automatic, each shows its reasoning in the console, and alerts fire when a decision is needed, not for every blocked message.

Microsoft supports layering. Its ICES Vendor Ecosystem documentation says integrating non-Microsoft email security vendors “supports a multi-layered defense strategy” and lists “defense in depth” as a benefit.

• Layer 1, Defender built-in protection: spam, bulk, known malware, spoofing. Keep it on.
• Layer 2, Defender Plan 1 or Plan 2: impersonation protection, Safe Links, Safe Attachments, and in Plan 2 investigation and response. Keep it on.
• Layer 3, Sentaro over the Microsoft 365 API: scores every inbound and internal message before interaction, blocks, quarantines or tags it inline, and covers the OAuth and AI-tool grants users create.

No MX change is involved, so mail routing and Defender policies stay as they are, and Sentaro can be removed the same way. Sentaro is not part of Microsoft’s ICES Vendor Ecosystem, so its verdicts appear in the Sentaro console and as mailbox labels, not in the Defender portal.

Defender figures are Microsoft’s standalone yearly-commitment list prices as of 18 October 2026; with Business Premium or E3, Plan 1 is already paid. Sentaro’s price includes every feature, and the roadmap vectors are included at no added cost (see the roadmap note). A protected account is one mailbox Sentaro watches; shared aliases and distribution lists do not count. The FBI IC3 puts the average reported BEC loss at about $123,000 (2025), so for most teams one avoided payment-fraud incident a year pays for the layer many times over.

• Payload-free fraud: vendor compromise, thread hijacking and bank-detail changes are scored from intent, relationship and thread context. Microsoft names no dedicated feature for vendor compromise.
• App risk included: every app, AI tool and OAuth grant inventoried, consent phishing blocked in mail flow, risky grants revoked, in every plan. Microsoft sells OAuth app governance separately in Defender for Cloud Apps.
• No security team needed: verdicts are automatic, each shows its reasoning in the console, and alerts fire only when a decision is needed.
• One engine for Microsoft 365 and Google Workspace, connected over API in four minutes with no MX change, and removable the same way.
• A Swedish vendor hosted in Sweden on Microsoft Azure, at $6 per protected account per month with every feature included. Prices in USD.

• Price and position: Plan 1 lists at $2 per user, is included in Business Premium and, from 2026, Microsoft 365 E3 and Office 365 E3, and decides delivery in the mail flow. Sentaro runs behind it and does not replace it.
• Native coverage: Safe Links, Safe Attachments and ZAP extend to Teams, SharePoint and OneDrive with no connector.
• Security-team tooling and response today: Plan 2 adds Threat Explorer, advanced hunting, AIR for compromised users and attack simulation training. Sentaro has no live equivalent for compromised-account response yet (see the roadmap note).
• Published commitments: Microsoft states a 99.999% monthly uptime SLA for built-in protection. Sentaro has not published an SLA; its certification status is in the note below.