Key Points:
- Microsoft 365 phishing attacks use lookalike emails and trusted branding to trick users, and default settings leave gaps.
- Strengthen protection by adding advanced filtering, tuned policies, safe links, MFA, user training, and DMARC monitoring.
- Managed email security closes gaps before and after delivery.
Phishing keeps using Microsoft 365 branding, lookalike domains, and “shared file” lures because users trust the platform. Attackers know many tenants stay on default settings. That leaves room for fake invoices, payroll changes, and MFA reset emails to land.
Strengthening Microsoft 365 phishing protection means keeping Microsoft in place, then adding inspection, identity-aware rules, and user defense on top. The result is fewer risky clicks, fewer credential thefts, and fewer wire transfers sent to the wrong account.
Why Microsoft 365 Needs Extra Email Security
Microsoft builds good baseline controls into Exchange Online Protection and Microsoft Defender for Office 365. You already get spam filtering, anti-malware, and preset anti-phishing policies.
Attackers do not aim at the baseline. They aim at the gaps. They spoof a CEO, copy an M365 notification, or reply inside an existing thread so the email looks normal. Verizon’s 2025 DBIR notes that human targets keep getting hit because phishing and pretexting stay cheap and effective.
FBI’s 2024 IC3 report tracked $2.77 billion in losses tied to business email compromise, which is mostly email impersonation. That means someone trusted the email enough to move money or data.
Common weak spots:
- Default policies stay on “standard,” not stricter levels.
- Inbound mail from external SaaS tools is trusted too early.
- VIP users are not protected with tighter impersonation settings.
- SOC teams see alerts but do not have automatic containment, which is where a managed security service keeps those alerts actionable.
Service-level email security solutions close those weak spots by adding controls before, alongside, and after Microsoft’s own filters.
Layers That Strengthen Microsoft 365 Phishing Protection
A good Microsoft 365 phishing protection stack keeps Microsoft in the center and surrounds it with more checks. Each layer blocks a tactic: fake sender, fake link, fake brand, or compromised account.
1. Advanced email filtering in front of M365.
An external secure email gateway or cloud email security tool inspects messages before Microsoft delivers them. It uses sender reputation, URL rewriting, file sandboxing, and AI-driven anomaly checks. This helps catch office 365 phishing email attempts that copy Microsoft wording but come from free mailboxes.
2. Tightened Defender anti-phishing policies.
You can raise the phishing threshold, enable mailbox intelligence, and protect VIPs and domain names from impersonation in the Defender portal. Many tenants never tune these policies, so a service offering can do it for you and keep it tuned.
3. Identity and MFA enforcement.
Phishing is often a step toward session theft. When email security works with conditional access, sign-in risk policies, or multi-factor authentication for Microsoft 365, attackers who do get a password still cannot log in.
4. Link and attachment protection.
Safe links and safe attachments style features detonate suspicious content in an isolated environment. That stops microsoft 365 phishing email payloads that look harmless at first but download malware later.
5. User-level training and reporting.
Email security is better when users can report suspicious messages from Outlook and those reports go to the service desk. This is especially true when users follow practical email security tips that lower ransomware risk. Verizon highlights the human element every year, so lowering user error lowers real risk.
6. DMARC, DKIM, SPF monitoring.
Attackers spoof your own domain to trick staff. A managed email security service can watch those records and alert when a phishing campaign starts using your brand.
When these pieces run together, microsoft 365 phishing protection moves from “filter spam” to “detect, block, and respond.”
How Service-Level Email Security Works Day to Day
Service-level means the provider does the tuning, monitoring, and incident handling for you. It is not a one-time “how to block phishing in Office 365” tutorial. It is ongoing protection.
Daily pattern looks like this:
- Inbound screening: Messages are checked against threat intel, sender reputation, and impersonation rules before the inbox.
- Policy-based decisions: Messages that target finance, HR, or executives are treated more strictly.
- User feedback loop: Reported emails are analyzed, and if malicious, similar messages are pulled from other inboxes.
- Account protection: If a user clicks and enters their password on a fake Microsoft page, the service triggers a password reset or account lock.
- Reporting to leadership: You get monthly or weekly views of blocked office 365 phishing, top impersonated users, and vendors that were spoofed.
Why this is important? The FBI said overall internet crime losses hit $16 billion in 2024 and rose 33% from the year before. Email is still one of the easiest ways in.
A managed approach gives you:
- Faster rollout of stricter Defender policies
- Fewer false positives because someone is watching the queues
- Quick clawback when a bad message was delivered
- Records for audits and cyber insurance
What Does Microsoft 365 Phishing Protection Miss?
Even with Defender’s Standard and Strict preset policies, Microsoft still has to balance usability with security. That leaves gaps a service can fill.
Gaps to address:
- Internal phish or compromised users. Default filters look hard at external mail. A compromised account sending inside the tenant may pass through.
- Vendor impersonation. Attackers copy the format of a known supplier, then ask AP to change bank details.
- Delayed payloads. Emails with links that turn malicious after delivery can bypass first inspection.
- Multi-channel lures. Some attacks send an email and a Teams or SharePoint notification to increase trust.
Service-level controls and enterprise cybersecurity safeguards can rescan delivered mail, integrate with SIEM tools, and share indicators with other security platforms. That makes the protection wider than pure office 365 phishing.
Frequently Asked Questions
How do I enable anti-phishing in Office 365?
Enable anti-phishing in Office 365 by opening the Microsoft Defender portal, selecting Email & Collaboration, then Threat policies, and choosing Anti-phishing. Create or edit a policy, assign it to users or groups, and set impersonation, mailbox intelligence, and actions to Standard or higher. Save and enable the policy to activate protection.
What is the default anti-phishing policy in Office 365?
The default anti-phishing policy in Office 365 is a built-in, always-on policy that applies basic protection to all cloud mailboxes. This policy runs before any custom or stricter preset policies. The default policy cannot be deleted, but administrators can apply higher-priority policies for VIPs or sensitive users.
Does Microsoft Defender protect against phishing?
Yes. Microsoft Defender for Office 365 protects against phishing using machine learning, domain impersonation detection, mailbox intelligence, safe links, and safe attachments. Protection improves when policies are tuned, URLs are rewritten, and users report suspicious emails. Additional service-level filtering further strengthens phishing detection and email security.
Strengthen Email Security for Your M365 Tenant
Lowering phishing risk is easier when email is filtered, tuned, and watched by specialists. A managed email security service in Cincinnati can add that inspection on top of Microsoft 365 so spoofed invoices, fake Microsoft 365 notifications, and vendor impersonation attempts are stopped early.
At LK Tech, we help organizations add the missing layers around Microsoft 365, from policy tuning to ongoing monitoring, so phishing and BEC attempts have fewer ways in. Contact us today to map out the protections your tenant still needs and set clear expectations on alerting, response, and end-user reporting.
