Microsoft 365 Security Mistakes Businesses Make

Microsoft 365 is one of the most widely used business platforms in the world, which also makes it one of the most targeted. Most businesses assume that because Microsoft built it, the default settings are secure enough. They're not.

Here are the most common Microsoft 365 security mistakes IIS finds during IT assessments.

1. Multi-Factor Authentication Isn't Enforced Everywhere

Multi-factor authentication, or MFA, is one of the single most effective ways to stop account takeovers, but many businesses only turn it on for a few users, or leave it optional. If even one account skips MFA, attackers have an open door.

2. Global Admin Accounts Are Overused

Every user with Global Admin access can change security settings, access all mailboxes, and control the entire tenant. Many businesses have far more Global Admins than they need, which multiplies the damage if any one of those accounts is compromised.

3. Conditional Access Policies Are Missing

Without conditional access, anyone with the right password can log in from anywhere in the world, on any device. Conditional access lets you restrict logins by location, device health, or risk level, a control most businesses never turn on.

4. Mailbox Forwarding Rules Go Unchecked

Attackers who gain access to a mailbox often set up silent forwarding rules to quietly copy incoming email, including invoices and payment details, to an external address. Without regular audits, these rules can run undetected for months.

5. License Features Go Unused

Many Microsoft 365 plans already include security tools like Defender, data loss prevention, and advanced threat protection, but businesses never turn them on because nobody configured them.

Why This Matters

Business Email Compromise attacks caused billions of dollars in reported losses in a single year, and most of those attacks start inside Microsoft 365 environments with weak configurations, not sophisticated hacking.

What To Do About It

A Microsoft 365 security review checks MFA enforcement, admin role assignments, conditional access, mailbox rules, and license utilization, then closes the gaps attackers are actively looking for.

Want to know if your M365 environment has these gaps? Book a Free IT Assessment and get a clear picture of where you stand.