Microsoft 365 gives businesses powerful tools for email, files, meetings and collaboration. Its flexibility also means that a tenant can accumulate risky settings, excessive permissions and forgotten access unless someone reviews it deliberately.
The exact options available depend on licensing and configuration. These ten areas provide a useful security review for most organisations.
1. Require modern multi-factor authentication
Protect all users, with particular attention to administrators, finance teams and remote workers. Prefer phishing-resistant methods where practical and control how new authentication methods are registered.
2. Block legacy authentication
Older sign-in protocols may not support modern controls. Identify whether any applications still depend on them, migrate those applications and block unnecessary legacy access.
3. Reduce administrator privileges
Keep the number of privileged accounts small. Use separate administrator identities, assign the least powerful role that meets the need and review assignments regularly. Emergency access accounts need strong protection and monitoring too.
4. Apply risk-based access rules
Conditional Access can respond to factors such as user, device, location and sign-in risk. Start with carefully tested policies and exclusions so stronger security does not accidentally lock out the whole organisation.
5. Review external sharing
Check how SharePoint, OneDrive and Teams allow information to be shared outside the business. Decide when anonymous links are acceptable, use sensible expiry periods and give site owners guidance they can follow.
6. Control automatic email forwarding
Attackers often create forwarding rules to monitor conversations after compromising a mailbox. Restrict automatic forwarding outside the organisation and investigate unexpected inbox rules and transport rules.
7. Configure domain email authentication
SPF, DKIM and DMARC help receiving systems identify messages legitimately sent for your domains. Deploy them carefully, monitor results and include every authorised sending service.
8. Keep audit and alert information useful
Confirm that relevant events are retained and someone receives actionable alerts. Important examples include suspicious sign-ins, privilege changes, unusual forwarding, mass downloads and changes to security settings.
9. Review applications and third-party consent
Connected applications can retain access to mailboxes and files without using a password. Review enterprise applications, delegated permissions and user consent. Remove abandoned integrations and challenge requests for broad access.
10. Test account recovery and incident procedures
Know how the business will respond to a compromised account, revoke sessions, reset credentials, review mailbox rules and preserve evidence. Helpdesk identity checks should be strong enough to resist social engineering.
Security is an ongoing process
Microsoft changes services regularly, employees come and go, and collaboration creates new access paths. Record your intended configuration, monitor exceptions and schedule recurring reviews instead of treating the tenant as a one-off setup.
Astley Digital helps businesses manage Microsoft 365 as part of a wider managed IT service. To discuss a security review, contact our UK team.
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