Most organizations assume Office 365 is secure “out of the box.” It isn’t.
By default, Microsoft provides a powerful platform — but very few security controls are fully enabled. Attackers know this, which is why Office 365 is one of the most targeted ecosystems for phishing, credential theft, business email compromise (BEC), and data exfiltration.
At Mindcore Technologies, we routinely harden Office 365 environments that were unintentionally left wide open. The problem isn’t Microsoft itself — the problem is misconfiguration, lack of monitoring, and the dangerous assumption that “someone else already secured it.”
If you use Office 365 for email, collaboration, storage, or identity management, these are the critical settings you must lock down immediately to protect your business.
1. Enforce Multi-Factor Authentication (MFA) for All Accounts
Office 365 accounts without MFA are the easiest possible targets.
Attackers use:
- Password spraying
- Credential stuffing
- Infostealer malware
- Session hijacking
…to bypass simple username/password logins.
Every user — especially admins — must have MFA enforced.
Best options:
- Authenticator App
- FIDO2 Hardware Keys
- Number Matching (strong protection)
Never rely on SMS MFA for executives or admins due to SIM-swapping risks.
2. Disable Legacy Authentication — Immediately
Legacy protocols like:
- IMAP
- POP
- SMTP AUTH
- MAPI
- ActiveSync
…completely bypass MFA, making your secure environment useless.
Microsoft reports over 99 percent of password spray attacks target legacy authentication.
Turn it off globally unless a specific, documented business need exists.
Mindcore Technologies disables legacy auth by default during every O365 hardening engagement.
3. Protect Global Admin Accounts with Strict Policies
Your Global Admins have the keys to your entire Microsoft ecosystem. They must be treated as high-risk identities.
Minimum protections:
- Zero shared admin accounts
- MFA required
- No admin performed from personal devices
- Admin accounts cannot access email
- Conditional Access with device compliance rules
- Dedicated administrative workstations
If your admins browse the internet or check email from their admin accounts, you’re one exploit away from a complete takeover.
4. Enable Conditional Access Policies
Conditional Access (CA) is the backbone of modern Office 365 security.
Use CA to enforce:
- MFA on all accounts
- Block risky sign-ins
- Require compliant or hybrid-joined devices
- Restrict access by country
- Block legacy authentication
- Prevent sign-ins from TOR, anonymous VPNs, or suspicious locations
Without Conditional Access, anyone with a password can attempt logins from anywhere on Earth.
5. Turn On Microsoft Defender for Office 365 Protections
Defender for Office 365 stops:
- Malicious attachments
- Zero-day malware
- Link-based attacks
- Spoofing attempts
Critical settings to enable:
- Safe Links (URL scanning)
- Safe Attachments (sandboxing)
- Anti-phishing policies
- User impersonation detection
- Domain impersonation protection
Mindcore sees most breaches start with a malicious email. Defender drastically reduces this risk.
6. Lock Down External Email Forwarding
Attackers often configure hidden forwarding rules so stolen mail silently gets sent to an outside inbox.
You must prevent:
- External automatic forwarding
- Inbox rules that hide messages
- Forwarding to personal accounts
Audit forwarding rules monthly — they are one of the top indicators of compromised mailboxes.
7. Enable Audit Logging and Mailbox Monitoring
If logging is not turned on, you have no visibility into:
- Suspicious login attempts
- Admin actions
- Data exports
- Email forwarding
- Permission changes
- Mailbox access by other users
Your security team needs this data to investigate attacks quickly.
Turn on:
- Unified Audit Logging
- Mailbox Audit Logging
- Admin Audit Logging
Without logs, incident response becomes guesswork.
8. Secure SharePoint and OneDrive Sharing Settings
By default, many tenants allow:
- Anonymous links
- External sharing
- Unrestricted file sharing
- Unlimited link expiration
These settings lead to accidental exposure of sensitive data.
Lock down:
- Who can share externally
- Link expiration rules
- Anonymous link restrictions
- Sensitivity labels for confidential data
Data loss often comes from misconfiguration, not hacking.
9. Implement Data Loss Prevention (DLP) Policies
DLP prevents users from accidentally (or intentionally) sending out sensitive data such as:
- Financial information
- Client data
- PHI or PII
- Credit card numbers
- Proprietary documents
Office 365 can automatically block, warn, or monitor risky data transfers.
Mindcore Technologies configures DLP rules tailored to industry requirements like HIPAA, FINRA, SOC 2, and PCI.
10. Review Admin Roles Regularly
Too many businesses assign Global Admin rights because it’s “easier.”
This is extremely dangerous.
Use least privilege:
- Global Admin
- Exchange Admin
- SharePoint Admin
- Teams Admin
- Security Admin
- Compliance Admin
Only assign what the user actually needs.
Revoke excess privileges every quarter.
11. Enable Alerts for Suspicious Activity
Office 365 can warn you when:
- Impossible travel logins occur
- A user signs in from risky IPs
- Mass forwarding is detected
- Malware is uploaded
- Excessive file downloads occur
- Multiple failed login attempts spike
These alerts allow you to react before damage is done.
Mindcore’s SOC monitors these events 24/7 for clients.
So, How Secure Is Office 365?
Office 365 can be extremely secure — but only if you configure it properly.
Out of the box, it is not secure enough for modern threat actors.
A hardened Office 365 environment includes:
✔ MFA enforced
✔ Legacy auth disabled
✔ Conditional Access
✔ Defender protection
✔ Admin isolation
✔ DLP and compliance policies
✔ Logging and monitoring
✔ Least-privilege role assignments
This configuration dramatically reduces the risk of account compromise, data theft, and business email fraud.
Mindcore Technologies: Hardening Office 365 for Real-World Threats
Mindcore helps organizations lock down Office 365 with:
- Full tenant security audits
- Conditional Access policy design
- DLP and compliance configuration
- Admin role restructuring
- Defender for Office 365 implementation
- SOC monitoring and threat response
- Zero-trust identity frameworks
Secure Office 365 is no longer optional — it’s foundational to protecting your business.
