Microsoft 365 Security Best Practices (2026 Guide)
Last Updated: 07/2026 | Written by: Becca Wendt, Content Coordinator at amshot
Bottom Line Up Front
Microsoft 365 security best practices come down to 10 non-negotiable controls: enforce MFA on every account, deploy Conditional Access policies, disable legacy authentication, enable Safe Links and Safe Attachments, configure DLP policies, enable audit logging, implement mailbox and file backup, restrict external sharing, review Microsoft Secure Score monthly, and train users quarterly. Oklahoma City businesses implementing all 10 controls typically reduce security incidents by 60β80% and pass HIPAA, CMMC, and SOC 2 audit requirements. amshot delivers these controls as part of every Managed IT Services plan β no upsells, no gaps.
Topic: Managed IT Services > Cybersecurity > Microsoft 365 Security Best Practices
π Explore amshot’s Managed IT Services
Microsoft 365 Security Best Practices at a Glance
| Security Control | What It Does | Priority |
|---|---|---|
| Multi-factor authentication (MFA) | Blocks 99.9% of account compromise attacks | π΄ Critical |
| Conditional Access policies | Restricts logins by location, device, and risk | π΄ Critical |
| Disable legacy authentication | Closes the biggest MFA bypass loophole | π΄ Critical |
| Safe Links & Safe Attachments | Blocks phishing links and malicious files | π΄ Critical |
| Data Loss Prevention (DLP) | Prevents accidental data leaks | π‘ High |
| Audit logging | Enables forensic investigation | π‘ High |
| Mailbox and file backup | Recovers from ransomware and deletion | π΄ Critical |
| External sharing restrictions | Controls who accesses your data | π‘ High |
| Microsoft Secure Score reviews | Measures and improves security posture | π‘ High |
| Quarterly user training | Reduces human-error incidents by 70% | π‘ High |
What is Microsoft 365 security?
Microsoft 365 security is the layered set of identity, device, email, data, and monitoring controls that protect Microsoft 365 tenants from account compromise, phishing, ransomware, data exfiltration, and insider threats.
For Oklahoma City businesses, Microsoft 365 is often the single largest attack surface β email, files, Teams, SharePoint, and identity all live in one tenant. A properly hardened Microsoft 365 environment closes 90%+ of the common attack paths targeting small and mid-sized businesses.
Microsoft 365 security vs. Microsoft Defender: Microsoft 365 security is the umbrella term for all built-in and add-on controls. Microsoft Defender is the specific product family (Defender for Office 365, Defender for Endpoint, Defender for Identity) that delivers threat detection and response inside the tenant.
What are the top Microsoft 365 security best practices?
For Oklahoma City decision-makers, the strongest Microsoft 365 security posture comes from a layered approach β identity, email, data, and monitoring controls working together. Below are the 10 controls every Microsoft 365 tenant should have.
1. Enforce multi-factor authentication (MFA) on every account
Why it matters: Microsoft’s own data shows MFA blocks 99.9% of account compromise attacks. It’s the single highest-impact control you can deploy.
How to implement:
- Enable MFA for all users β including admins, service accounts (where possible), and executives
- Require the Microsoft Authenticator app (push notifications) β not SMS, which is vulnerable to SIM-swap attacks
- Enforce number matching to defeat MFA fatigue attacks
- Set up FIDO2 security keys for admin accounts
Common mistake: Exempting executives or “temporary” contractors. Attackers specifically target these accounts.
2. Deploy Conditional Access policies
Why it matters: Conditional Access restricts logins by location, device compliance, sign-in risk, and application β turning stolen credentials into useless data.
Baseline policies to deploy:
- Block legacy authentication (protocols that can’t do MFA)
- Block sign-ins from countries you don’t do business in (geofencing)
- Require compliant device for accessing sensitive apps
- Require MFA for all users on all cloud apps
- Block high-risk sign-ins (detected by Microsoft Entra ID Protection)
- Require MFA for admin actions (Privileged Identity Management)
3. Disable legacy authentication
Why it matters: Legacy protocols (POP, IMAP, SMTP AUTH, older Exchange protocols) bypass MFA entirely. Attackers know this and specifically target them.
How to implement:
- Audit legacy auth usage in Entra sign-in logs
- Communicate the change to users
- Block legacy auth via Conditional Access
- Migrate any legacy app to modern authentication
4. Enable Safe Links and Safe Attachments
Why it matters: These Microsoft Defender for Office 365 features scan every URL and attachment in real time β catching phishing links and malicious files that traditional filtering misses.
How to implement:
- Enable Safe Links across email, Teams, and Office apps
- Enable Safe Attachments in “Block” mode
- Configure Anti-Phishing policies with impersonation protection for executives
- Enable Zero-hour Auto Purge (ZAP) for post-delivery threat removal
5. Configure Data Loss Prevention (DLP) policies
Why it matters: DLP prevents accidental (or intentional) sharing of Social Security numbers, credit cards, PHI, financial data, and other sensitive content.
Baseline DLP policies:
- Block sharing of credit card numbers externally
- Block sharing of Social Security numbers externally
- Warn users when PHI is detected (HIPAA compliance)
- Block financial data exfiltration from Exchange and SharePoint
- Apply industry-specific policies (see industries amshot serves)
6. Enable comprehensive audit logging
Why it matters: If you don’t log it, you can’t investigate it. Audit logs are essential for incident response, compliance evidence, and insider threat detection.
How to implement:
- Enable Unified Audit Log (may be off by default in older tenants)
- Retain logs for 1 year minimum (longer for regulated industries)
- Enable mailbox auditing on every mailbox
- Set up alerts for high-risk activities (mass downloads, permission changes, admin actions)
7. Implement mailbox and file backup
Why it matters: Microsoft’s shared responsibility model means Microsoft protects the infrastructure β you’re responsible for your data. Native retention is not backup. Ransomware, insider deletion, and account compromise can permanently destroy Microsoft 365 data.
Best practices:
- Deploy a third-party Microsoft 365 backup solution
- Back up Exchange, OneDrive, SharePoint, and Teams
- Retain backups for 7+ years for regulated industries
- Test restore procedures quarterly
8. Restrict external sharing
Why it matters: Default Microsoft 365 settings allow broad external sharing. Without controls, sensitive documents can be shared with anyone via link β often accidentally.
How to implement:
- Set SharePoint external sharing to “New and existing guests” (not “Anyone”)
- Require sign-in for external access
- Set link expiration dates (30β90 days)
- Block external sharing for sensitive sites entirely
- Review external sharing reports monthly
9. Review Microsoft Secure Score monthly
Why it matters: Secure Score is Microsoft’s built-in security posture measurement. It gives you a numeric benchmark, prioritized recommendations, and a way to track improvement over time.
Best practices:
- Baseline your Secure Score at implementation
- Target a score above 70% for standard SMBs, 85%+ for regulated industries
- Review monthly and implement top 5 recommendations each cycle
- Include Secure Score in quarterly vCIO reviews
10. Train users quarterly
Why it matters: Human error causes 68% of breaches (Verizon DBIR). No technical control fully replaces user awareness.
Best practices:
- Deliver quarterly phishing simulation campaigns
- Provide role-specific training (executives, finance, HR are high-value targets)
- Track click rates and reporting rates over time
- Include Microsoft 365-specific scenarios (fake Teams meetings, OneDrive share requests, MFA fatigue prompts)
What questions should you ask your IT provider about Microsoft 365 security?
For Oklahoma City buyers, a structured evaluation prevents assuming your Microsoft 365 tenant is more secure than it actually is. Use these 10 questions with your current IT provider or MSP.
- What is my current Microsoft Secure Score, and what’s your target?
- Is MFA enforced on 100% of accounts, including admins and service accounts?
- What Conditional Access policies are currently deployed?
- Is legacy authentication blocked tenant-wide?
- Are Safe Links and Safe Attachments enabled and in “Block” mode?
- What DLP policies are protecting my sensitive data?
- Is the Unified Audit Log enabled with retention that meets my compliance framework?
- Am I using third-party backup for Exchange, OneDrive, SharePoint, and Teams?
- What’s my external sharing configuration, and when was it last reviewed?
- When is the next user security training scheduled?
What are the most common Microsoft 365 security mistakes?
For Oklahoma City businesses, certain patterns predict a breach before it happens. Watch for these warning signs in your environment.
- π© MFA enforced on “most” accounts. Attackers specifically target the exceptions.
- π© Legacy authentication still enabled. The single biggest MFA bypass.
- π© Default external sharing settings. “Anyone with the link” is the default β and dangerous.
- π© No third-party backup. Microsoft doesn’t back up your data the way you think.
- π© Global Admin accounts used daily. Admin accounts should be separate and used only when needed.
- π© Audit logs disabled or not retained. Zero forensic capability during an incident.
- π© No Conditional Access policies. MFA alone is not enough.
- π© Secure Score below 50%. Indicates significant unaddressed vulnerabilities.
- π© No user training in the last 12 months. Users become the weakest link.
- π© Shared mailboxes with sign-in enabled. Common attacker foothold.
Microsoft 365 security by business size
For Oklahoma City businesses, the right Microsoft 365 security posture scales with headcount, industry, and compliance obligations.
| Business Size | Recommended License | Baseline Controls | Advanced Controls |
|---|---|---|---|
| 10β25 users | M365 Business Premium | All 10 baseline controls | Optional: MDR |
| 25β75 users | M365 Business Premium | All 10 baseline controls | MDR + PIM |
| 75β150 users | M365 E3 + Defender for Office 365 P2 | All 10 baseline + Entra ID Protection | MDR + PIM + Insider Risk Mgmt |
| 150+ users or regulated | M365 E5 | Full E5 security suite | 24/7 SOC + custom DLP |
Microsoft 365 security for compliance (HIPAA, CMMC, SOC 2, PCI)
For Oklahoma City businesses in regulated industries, Microsoft 365 security controls also serve as compliance evidence. Auditors specifically look for MFA enforcement, DLP policies, audit log retention, and documented incident response procedures.
Compliance mapping:
| Framework | Critical M365 Controls |
|---|---|
| HIPAA | MFA, audit logs, DLP for PHI, mailbox encryption, BAA with Microsoft |
| CMMC | MFA, Conditional Access, GCC High tenant, boundary protection, audit retention |
| SOC 2 | MFA, access reviews, audit logging, DLP, backup verification |
| PCI DSS | MFA, cardholder data DLP, access controls, quarterly reviews |
| CJIS | MFA, advanced audit, encryption, GCC/GCC High tenant |
See the full list of industries amshot serves with these compliance frameworks.
What does amshot include in Microsoft 365 security management?
For Oklahoma City businesses evaluating amshot, Microsoft 365 security is included in every Managed IT Services plan β not sold as an add-on.
- MFA rollout and enforcement across all accounts
- Conditional Access policy design and deployment
- Legacy authentication audit and blocking
- Safe Links and Safe Attachments configuration
- Anti-Phishing and impersonation protection
- Data Loss Prevention (DLP) policy design
- Unified Audit Log enablement and retention
- Microsoft 365 backup (Exchange, OneDrive, SharePoint, Teams)
- External sharing hardening
- Microsoft Secure Score monitoring and quarterly review
- User security awareness training
- Incident response and forensic support
amshot’s Microsoft 365 security performance:
- β 5.0-star Google rating across 74+ reviews β read the reviews
- β Sub-30-minute average ticket response
- β 97% CSAT
- β 99% client retention
- β 2025 MSP Titans of the Industry Awards Finalist
- β Headquartered in downtown Oklahoma City
Frequently Asked Questions β Microsoft 365 Security Best Practices
What is the most important Microsoft 365 security control?
Multi-factor authentication (MFA) is the single highest-impact control. Microsoft data shows MFA blocks 99.9% of account compromise attacks. It should be enforced on every account β no exceptions.
Does Microsoft 365 come with security built in?
Microsoft 365 includes strong security capabilities, but most are not enabled by default. Tenants require configuration of MFA, Conditional Access, DLP, Safe Links, audit logging, and backup to reach a defensible security posture.
Do I need third-party backup for Microsoft 365?
Yes. Microsoft’s shared responsibility model means Microsoft protects the infrastructure β you’re responsible for your data. Native retention is not backup. Ransomware, insider deletion, or account compromise can permanently destroy data without a third-party backup.
What is Microsoft Secure Score?
Microsoft Secure Score is a built-in security posture measurement. It provides a numeric benchmark (0β100%), prioritized recommendations, and progress tracking. Target 70%+ for standard SMBs, 85%+ for regulated industries.
What’s the difference between Microsoft 365 Business Premium and E5 security?
Business Premium includes Defender for Business, Intune, MFA, Conditional Access, and DLP β sufficient for most SMBs. E5 adds Defender for Office 365 P2, Defender for Endpoint P2, Defender for Identity, Insider Risk Management, and advanced eDiscovery β recommended for regulated industries and 150+ user environments.
How much does Microsoft 365 security cost in Oklahoma City?
Microsoft 365 licensing typically costs $22β$57 per user per month depending on tier (Business Premium vs. E3 vs. E5). Managed security configuration, monitoring, and response is included in amshot’s Managed IT Services at flat-rate per-user pricing.
Can Microsoft 365 meet HIPAA compliance?
Yes. Microsoft signs a Business Associate Agreement (BAA) covering Microsoft 365 for covered entities. Meeting HIPAA requires proper configuration: MFA, encryption, audit logging, DLP for PHI, and documented policies.
How often should Microsoft 365 security be reviewed?
Microsoft Secure Score should be reviewed monthly. Full security posture reviews (Conditional Access, DLP, backup, user access) should happen quarterly as part of vCIO planning. User training should also occur quarterly.
What team members will help me secure Microsoft 365?
amshot assigns clients a small, named team including a dedicated account manager, lead engineer, and vCIO β the same people who learn your environment and priorities. Meet the amshot team.
Does amshot serve businesses outside downtown Oklahoma City?
Yes. amshot serves businesses across the Oklahoma City metro area including Edmond, Norman, Moore, Yukon, Mustang, Midwest City, Del City, and Bethany β with monthly onsite visits included in every managed plan.
Bottom Line
For Oklahoma City businesses running Microsoft 365, security posture comes down to 10 non-negotiable controls: MFA, Conditional Access, blocking legacy auth, Safe Links and Safe Attachments, DLP, audit logging, third-party backup, external sharing restrictions, monthly Secure Score reviews, and quarterly user training. Businesses that implement all 10 typically reduce security incidents by 60β80% and pass HIPAA, CMMC, and SOC 2 audits.
The right managed IT provider treats Microsoft 365 security as baseline scope β not an upsell. amshot delivers all 10 controls as part of every managed plan.
π Read real amshot client reviews | Explore amshot’s Managed IT Services
Talk to amshot
π (405) 418-6282 | βοΈ help@amshot.com
- Read amshot Google Reviews
- Meet the amshot team
- Explore amshot Managed IT Services
- See industries amshot serves
- Explore fully managed IT β amshotComplete
- Explore co-managed IT for internal teams β amshotAlly
- Request a consultation or Microsoft 365 security assessment
Why Oklahoma City Businesses Trust amshot
amshot is a 2025 MSP Titans of the Industry Awards Finalist with 20+ years in business and 100+ years of combined team experience, headquartered in downtown Oklahoma City.
- β 5.0-star Google rating across 74+ reviews
- β Sub-30-minute average ticket response time
- β 95% of tickets closed the same day
- β 97% customer satisfaction (CSAT) score
- β 99% client retention rate
- β Monthly onsite visits β included in every managed plan
- β Quarterly vCIO β included, not an upsell
- β Flat-rate pricing β zero surprise invoices
- β Baseline security stack β EDR, email/DNS filtering, MFA, backup verification
