How to Secure Your Microsoft 365 Environment

Microsoft 365 holds email, files and identities for many businesses, which makes it a prime target. Much of its security depends on how it is configured. These steps close the most common gaps.

Require multi-factor authentication

Enforce MFA for every user, and prefer phishing-resistant methods such as authenticator apps with number matching or security keys. Start with administrators.

Block legacy authentication

Older sign-in protocols can't enforce MFA. Block them with Conditional Access or security defaults so attackers can't go around your sign-in protections.

Protect administrator accounts

Keep the number of global administrators small, use dedicated admin accounts that aren't used for everyday email and assign the least-privileged role that gets the job done.

Use Conditional Access

Where your licensing allows, create policies that consider the user, device, location and sign-in risk, such as requiring a managed device to reach sensitive data.

Harden email

Configure SPF, DKIM and DMARC, turn on anti-phishing and attachment protections and block automatic forwarding to external addresses, a common sign of a compromised mailbox.

Control sharing

Review SharePoint and OneDrive external sharing settings. Limit links that anyone can open, set expiration dates and audit what is already shared.

Turn on auditing and alerts

Confirm audit logging is enabled and set alerts for suspicious activity, such as unusual sign-ins, new inbox rules and large file downloads.

Back up your data

Microsoft keeps the service running, but protecting your data is a shared responsibility. Consider a dedicated backup for mail, OneDrive, SharePoint and Teams.

Review regularly

Use Microsoft Secure Score as a starting point, and revisit your configuration as Microsoft adds features and your business changes.