Microsoft 365 runs the daily work for many Phoenix organisations, email, Teams, SharePoint, OneDrive, and cloud identity. That also makes it one of the most targeted platforms for phishing, account takeover, and business email compromise.
The good news is you can reduce risk quickly with a clear baseline. Use the checklist below to tighten security, improve visibility, and protect business data.
Why Microsoft 365 security matters
Most modern incidents do not start with a “hack”. They start with:
a stolen password
an employee tricked by a realistic login prompt
a weak admin setup
risky sign ins from unmanaged devices
mailbox rules that hide attacker activity
A solid Microsoft 365 security setup reduces these common attack paths and supports compliance and cyber insurance expectations.
Microsoft 365 security checklist
1) Enforce MFA for every user
MFA is the most important control for reducing account takeover risk.
Best practice
Require MFA for all users, not just admins
Prefer app based authenticators
Use stronger rules for privileged users
2) Add Conditional Access policies
Conditional Access lets you block risky sign ins and control access based on context.
Start with
Block legacy authentication
Require MFA for all cloud apps
Require compliant device for sensitive apps or file access
Block sign ins from countries you do not operate in, when practical
Apply stricter rules for admins
3) Protect admin accounts properly
Admin compromise is one of the fastest routes to organisation wide impact.
Do this
Use separate admin accounts, do not browse or email on admin profiles
Reduce the number of global admins
Enable stronger sign in rules for admin roles
Monitor admin role changes
4) Turn on mailbox auditing and alerting
Attackers often create mailbox rules and forwarding to hide activity.
Watch for
new forwarding rules
suspicious inbox rules that delete or move emails
unusual sign in locations
mass sending behaviour
5) Improve phishing protection
Email remains a top entry point.
Strengthen with
advanced phishing and malware filtering
safe links and attachment scanning
impersonation protection where available
user reporting tools, make it easy to report suspicious email
6) Implement SPF, DKIM, and DMARC
These reduce domain spoofing and help protect clients and vendors from impersonation.
Rollout tip
start with DMARC monitoring
then move toward quarantine
then reject when legitimate senders are verified
7) Control access to SharePoint and OneDrive
Sensitive files should not be accessible from unmanaged devices without guardrails.
Consider
limiting downloads on unmanaged devices
requiring compliant devices for document libraries with sensitive data
reviewing external sharing links and expiry settings
using least privilege by team and role
8) Use device management for laptops and mobiles
If devices are unmanaged, security becomes inconsistent.
Minimum baseline
full disk encryption on laptops
patching and update policies enforced
screen lock policies
endpoint protection, ideally EDR
ability to wipe lost devices
9) Add data protection policies for sensitive information
Many businesses handle data that should not leave the organisation casually.
Examples
policies for financial data, legal client files, PHI
restrictions for sharing outside approved domains
alerts when sensitive data is shared externally
10) Back up Microsoft 365 data properly
Microsoft 365 has retention features, but many organisations still benefit from dedicated backup for fast recovery and longer retention needs.
Think about
mailbox and OneDrive recovery needs
SharePoint versioning and restore speed
legal hold requirements
ransomware scenarios, including mass deletion
11) Review sign in and security reports monthly
Security improves when you consistently review what is happening.
Monthly review items
risky sign ins and blocked attempts
user MFA status
admin role assignments
external sharing activity
DMARC reports
Quick self check, are you exposed?
You may be at higher risk if:
MFA is optional or only for some users
legacy authentication is still enabled
admins use one account for everything
external sharing is open by default
forwarding rules are not monitored
there is no routine review of sign ins and alerts
