Microsoft 365 Security Best Practices
Microsoft 365 sits at the center of many businesses. Email flows through Outlook, employees collaborate in Teams, documents live in OneDrive and SharePoint, and users may access company information from multiple devices and locations.
That convenience also makes Microsoft 365 accounts valuable targets for cybercriminals.
A stolen password, successful phishing email, overly broad administrator account, or poorly managed device can potentially give an attacker access to far more than a single application.
Securing Microsoft 365 isn’t about finding one setting that makes your business safe. A stronger environment uses multiple layers of protection across identities, email, devices, data, applications, and the people using them.
1. Make Multi-Factor Authentication a Standard, Not an Extra
Passwords alone aren’t enough protection for important business accounts.
If an attacker obtains an employee’s password through phishing, credential theft, password reuse, or another method, multi-factor authentication adds another barrier before the account can be accessed.
With MFA enabled, a login may require an additional verification method beyond the password.
However, simply turning MFA on isn’t the end of the conversation.
Employees should also understand that an unexpected authentication request can itself be a warning sign. If someone receives an MFA prompt when they aren’t attempting to sign in, they should deny the request and report it rather than approving it to make the notification disappear.
For particularly sensitive or privileged accounts, businesses should also evaluate stronger authentication methods rather than relying exclusively on basic password-based authentication.
2. Protect the Front Door: Your Business Email
One of the most important areas to protect in Microsoft 365 is also one employees use constantly: email.
Attackers can use phishing, impersonation, malicious attachments, fake Microsoft login pages, business email compromise, and other techniques to convince employees to hand over credentials, transfer money, or expose company information.
Microsoft 365 email security should therefore go beyond simply filtering obvious junk mail.
Businesses should think about:
- Phishing and impersonation protection
- Malicious links and attachments
- Spoofing
- Suspicious forwarding rules
- Account compromise
- Domain authentication
- Unusual sending activity
- Employee reporting procedures
Your domain’s SPF, DKIM, and DMARC configuration also plays an important role in authenticating legitimate email and reducing opportunities for domain spoofing.
Email security works best when technical protections and employee awareness work together.
3. Stop Giving Everyone More Access Than They Need
Microsoft 365 security isn’t only about keeping outsiders out. It’s also about controlling what authenticated users can access once they’re inside.
An employee in accounting probably doesn’t need the same access as an administrator. A temporary employee may not need access to every SharePoint site. And everyday user accounts generally shouldn’t receive administrative privileges simply because it’s convenient.
This is the idea behind least privilege: users receive the level of access necessary to perform their responsibilities without automatically receiving access to everything else.
Periodically review:
- Administrator accounts
- Microsoft 365 roles
- SharePoint permissions
- Shared mailboxes
- Distribution and Microsoft 365 groups
- External users
- Third-party application access
- Former employee accounts
This can limit unnecessary exposure and reduce the potential impact if an individual account becomes compromised.
4. Treat Administrator Accounts Differently
Not every Microsoft 365 account carries the same level of risk.
An attacker who compromises an ordinary employee account may gain access to that user’s resources. An attacker who gains control of a highly privileged administrator account could potentially make changes across a much larger portion of the Microsoft environment.
That makes administrator access worth protecting separately.
Organizations should limit administrative privileges to employees who genuinely require them, periodically review who has those privileges, and avoid using highly privileged accounts for routine activities when possible.
Administrative accounts should also have strong authentication protections and be monitored for suspicious activity.
The bigger the keys, the more carefully you should protect them.
5. Don't Forget About the Devices Accessing Microsoft 365
Your Microsoft environment can be well configured while an employee’s device remains a weak point.
Employees may access Outlook, Teams, OneDrive, and other Microsoft services from laptops, desktops, phones, and remote locations. Each device becomes part of your overall security picture.
Businesses should establish expectations around:
- Device updates and patching
- Endpoint protection
- Device encryption
- Screen locking
- Approved devices
- Lost or stolen equipment
- Personal devices
- Remote access
- Malware protection
Depending on your Microsoft licensing and environment, device-management and access-control capabilities can also help organizations establish requirements for devices accessing company resources.
The goal is to avoid treating Microsoft 365 security and endpoint security as two completely separate things.
6. Pay Attention to How Company Data Is Being Shared
OneDrive and SharePoint make collaboration much easier, but convenient sharing can also create unintended exposure.
Employees may send public or external links, share documents with vendors, grant access to entire folders, or leave old external permissions in place long after a project ends.
That doesn’t mean external sharing should simply be disabled across the board. Businesses need a sharing strategy that balances collaboration with control.
Consider questions such as:
- Who is allowed to share information externally?
- What types of company information should never be publicly shared?
- How long should external users retain access?
- Can employees see who currently has access to a document?
- What happens when a project or vendor relationship ends?
Periodically reviewing external access can uncover old permissions that nobody realized were still active.
7. Build Security Into Employee Onboarding AND Offboarding
Microsoft 365 security starts the moment an employee receives an account and it doesn’t end until their access has been properly removed.
When someone joins: Their account should receive the appropriate license, permissions, MFA configuration, application access, groups, and security policies based on their role.
Avoid simply copying another employee’s access because they have a similar job title. That can quietly carry unnecessary permissions from one person to another.
When someone leaves: The organization should have a documented process for addressing:
- Account access
- Active sessions
- OneDrive data
- Shared files
- Group memberships
- Devices
- Application access
- Licensing
- Ownership of business information
This is particularly important for employees with access to sensitive information or administrative systems.
An account belonging to someone who left six months ago shouldn’t remain active simply because nobody remembered to remove it.
8. Teach Employees What Microsoft-Themed Phishing Looks Like
Some of the best Microsoft 365 security controls can still be undermined by a convincing phishing message.
Attackers know that employees recognize Microsoft branding, which is why fake Microsoft alerts, password expiration notices, shared-document invitations, voicemail notifications, and login pages can be effective phishing lures.
Employees should know how to recognize warning signs such as:
- Unexpected password-reset requests
- Urgent account-expiration warnings
- Unexpected MFA prompts
- Suspicious shared-document links
- Login pages reached through unsolicited emails
- Messages asking for credentials
- Unusual requests from executives or coworkers
- Changes to payment or banking information
Security awareness training shouldn’t simply tell employees to “be careful.” It should teach them what suspicious activity looks like and what to do when they see it.
Employees should also have an easy, established way to report suspicious messages.
9. Know What Microsoft 365 Is and Isn't Doing With Your Data
One area businesses frequently overlook is data recovery.
Microsoft provides retention, recovery, and resiliency capabilities across Microsoft 365 services, but organizations still need to understand what information they have, how long it needs to be retained, and how it would be recovered after accidental deletion, malicious activity, account removal, or another incident.
Ask:
- What happens if an employee accidentally deletes important information?
- How long can deleted information be recovered?
- What happens to data when an employee account is removed?
- What business information needs longer retention?
- How would data be recovered after a cyber incident?
- Does our organization require additional backup capabilities?
Backup and Microsoft 365 security aren’t identical, but they are closely connected through business continuity and recovery.
10. Monitor for the Things That Shouldn't Be Happening
Security shouldn’t depend entirely on discovering an attack after an employee complains that something looks strange.
Businesses should have a way to identify and respond to suspicious Microsoft 365 activity.
Depending on your environment and licensing, signs worth investigating can include:
- Unusual login activity
- Suspicious geographic access
- Repeated failed login attempts
- Unexpected MFA activity
- New mailbox forwarding rules
- Changes to administrative privileges
- Suspicious email activity
- Unexpected third-party application access
Monitoring is particularly valuable because account compromises aren’t always obvious.
An attacker doesn’t necessarily need to immediately lock an employee out of their account. They may attempt to remain unnoticed while monitoring email, accessing information, or preparing for another attack.
The sooner unusual activity is identified, the sooner your organization can investigate it.
There isn’t one Microsoft 365 setting that makes an organization secure. Think of your environment as several connected layers:
Identity
Who is accessing Microsoft 365 and how are they proving who they are?
Access
What can each account actually reach?
Email
What protections exist against phishing, spoofing, malicious links, and impersonation?
Devices
Are the computers and phones accessing company information properly protected?
Data
Where is company information stored, who can share it, and how can it be recovered?
People
Do employees know how to recognize and report suspicious activity?
Monitoring
Would you know if something unusual happened?
Weakness in one layer can undermine protections elsewhere. That’s why Microsoft 365 security works best as part of a broader cybersecurity strategy rather than as a collection of individual settings.
A Quick Microsoft 365 Security Checklist
If you’re reviewing your environment, start with these questions:
- Is MFA required for our users?
- Are administrator privileges limited?
- Have we reviewed old or unused accounts?
- Are former employees properly removed?
- Are SPF, DKIM, and DMARC configured?
- Are endpoints properly secured and updated?
- Do we periodically review SharePoint and external sharing?
- Are employees trained to recognize phishing?
- Do we understand our Microsoft 365 backup and recovery strategy?
- Are suspicious logins and account activity being monitored?
If you can’t confidently answer several of these questions, that’s a good indication that your Microsoft 365 security configuration deserves a closer look.
Is Your Microsoft 365 Environment Properly Secured?
Microsoft 365 gives businesses powerful tools for communication, collaboration, and productivity, but protecting that environment requires more than creating employee accounts and turning on a few security settings.
Accounts, email, devices, permissions, data, employees, and monitoring all play a role in reducing risk.
Our Microsoft 365 Services can help businesses manage and support their Microsoft environment while connecting Microsoft 365 to their broader IT and cybersecurity strategy.
