Microsoft 365 is brilliant for small and medium businesses.
Email, files, Teams, collaboration – all in one place, accessible from anywhere.
But there’s a problem.
Most UK SMEs only scratch the surface of the security tools built into Microsoft 365. Worse, some businesses actually weaken their security with risky settings and “quick fixes” that never get revisited.
In this article, we’ll walk through five common Microsoft 365 security mistakes we see all the time – and what you can do to fix them before they become a real incident.
Mistake 1: Not Enforcing Multi-Factor Authentication (MFA) for All Users
Let’s start with the big one.
Many SMBs still rely on just a username and password to protect access to email, Teams and files. That’s fine until:
Someone reuses their work password on another breached site
A user is tricked by a phishing email and gives up their credentials
An attacker guesses or buys a password on the dark web
Once an attacker has a valid username and password, they can log straight into your Microsoft 365 tenant from anywhere in the world.
Without MFA, there’s almost nothing stopping them.
How to Fix It
- Make MFA non-negotiable
Enable MFA for all users, including directors and VIPs (they’re often the most targeted). - Use modern methods
Favour the Microsoft Authenticator app, push notifications or stronger options like FIDO keys where appropriate, rather than just SMS codes. - Introduce it in phases if needed
Start with higher-risk roles, then expand to everyone. Communicate clearly so users understand why you’re doing it. - Combine with Conditional Access
Use Conditional Access to refine rules (e.g. block older auth methods, require MFA for risky sign-ins or from unknown locations).
If you’re not sure where to start, a Microsoft 365 security review will quickly show you who has MFA enabled and who doesn’t.
Mistake 2: Leaving Legacy & Insecure Authentication Enabled
Even when MFA is enabled, many tenants still have legacy protocols and insecure authentication methods turned on, such as:
- IMAP
- POP
- SMTP AUTH (where not required)
- Old Office clients that don’t support modern authentication
These bypass modern security controls and can allow attackers to:
- Abuse mailboxes for spam and phishing
- Use “app passwords” to sneak in around MFA
- Maintain access in ways that are harder to detect
How to Fix It
- Audit what’s actually being used
Check which protocols and clients are in use. Some older tools or copiers may legitimately need them – most won’t. - Disable what you don’t need
Turn off legacy protocols at the tenant level where possible. Only keep exceptions where truly necessary, and log who/what they are for. - Upgrade old clients
Make sure staff are using supported, modern Office / Outlook builds that support modern authentication. - Review regularly
As you replace old systems, shrink the exception list until legacy auth is gone.
This is an easy win that dramatically reduces attack surface – and it can usually be done with minimal user impact if planned correctly.
Mistake 3: Allowing “Any Device, Anywhere” Without Controls
Microsoft 365 is accessible from almost any device with a browser or app. Great for productivity. Terrible if you:
- Have no idea which devices are accessing your data
- Don’t know if those devices are encrypted or patched
- Allow sign-ins from unmanaged, personal laptops with weak security
This is especially risky in remote and hybrid setups.
How to Fix It
The fix here is about combining Intune and Conditional Access with a sensible device strategy.
- Decide your device policy
- What’s allowed? Company-owned only? BYOD with controls?
- What’s the minimum standard for a device to be “trusted”?
- Use Microsoft Intune for device compliance
- Enforce encryption (e.g. BitLocker on Windows)
- Require a PIN/password and endpoint protection
- Keep OS and security patches up to date
- Use Conditional Access to control access
- Only allow access to Microsoft 365 from compliant devices (or give limited access to web-only on unmanaged devices, depending on risk appetite).
- Block sign-in from unsupported or risky platforms if needed.
- Handle BYOD properly
- Use Mobile Application Management (MAM) where possible, so you can wipe business data from personal devices without touching personal content.
This is where many SMEs benefit from help – designing and rolling out a sensible, staged Intune & Conditional Access strategy rather than switching it all on in one hit and breaking everything.
Mistake 4: Ignoring Secure Score and Built-In Microsoft 365 Security Insights
Microsoft gives you a handy tool called Secure Score in the Microsoft 365 Defender portal.
It:
- Analyses your current settings and configurations
- Gives you a score based on how secure your tenant is
- Suggests specific actions to improve security
Most SMEs don’t even know it exists – or they look once, get scared, and never return.
How to Fix It
- Actually open Secure Score
Go into the Microsoft 365 Defender portal and check your current score. - Triage the recommendations
- Not every suggestion needs doing immediately
- Focus first on high-impact, low-disruption actions:
- Enforce MFA
- Disable legacy auth
- Enable baseline alerting
- Tighten external sharing
- Treat it as a continuous improvement tool
Don’t obsess over getting to 100%. Use Secure Score as a guide to keep making regular, manageable improvements. - Document and review
Keep a simple log of what you’ve changed and why – useful for internal governance and external audits/clients.
Many Ash Bee Cloud security engagements start with Secure Score as the backbone for a prioritised security roadmap.
Mistake 5: Assuming “It’s in Microsoft 365, So It’s Backed Up”
This one is sneaky because it feels true.
You’ve moved your email to Exchange Online, your files to OneDrive and SharePoint, and your chat and documents sit in Teams. Microsoft has huge, resilient data centres.
Surely that means you don’t need backup… right?
Not quite.
Microsoft 365 has retention features, recycle bins and versioning – but that’s not the same as independent backup.
You can still permanently lose data due to:
- Accidental deletion that goes unnoticed for weeks or months
- Malicious deletion by a disgruntled user or compromised account
- Sync issues or mass changes that propagate everywhere
- Ransomware or other malicious activity affecting cloud-stored data
How to Fix It
- Accept that retention ≠ backup
See Microsoft’s own shared responsibility model – customers are still responsible for their data. - Implement a dedicated Microsoft 365 backup solution
One that can protect:- Exchange Online mailboxes
- SharePoint sites and document libraries
- OneDrive for Business accounts
- Teams data (where supported)
- Set sensible retention policies
- Shorter retention for general day-to-day recovery
- Longer retention (years) for emails/files in HR, finance, legal, etc.
- Test restores
Don’t just assume it works – regularly test restoring mailboxes, files and folders.
For most SMEs, Microsoft 365 backup is not expensive compared to the potential cost of lost emails, contracts or financial records.
- Bonus Mistake: Treating Security as a One-Off Project
Many businesses do a “big security push” once:- They switch on MFA.
- They tick a few boxes.
- They maybe run some awareness training.
Then it quietly drops down the priority list.
Meanwhile:
- New staff join without going through the same onboarding process.
- New tools and apps get added.
- Devices change.
- Threats evolve.
- Security isn’t a “do it once and forget it” job. It’s a process.
How to Fix It - Schedule regular security reviews (quarterly is a good start).
- Build security into onboarding/offboarding procedures.
- Review Secure Score and Conditional Access policies on a schedule.
- Treat backup and incident response as living plans, not documents in a drawer.
What Should You Do If You Recognise Yourself in These Mistakes?
If you read this and thought:
- “We don’t have MFA everywhere.”
- “I have no idea if we’re using legacy auth.”
- “We definitely don’t have a proper Microsoft 365 backup.”
You’re very much not alone – this is normal for many UK SMEs.
The good news: all of these issues are fixable with the right plan.
How Ash Bee Cloud Helps Fix Microsoft 365 Security for UK SMEs
Ash Bee Cloud is a Microsoft-focused MSP based in Gravesend, Kent, working with small and medium businesses across the UK.
Our Cyber Security & Microsoft 365 Compliance services typically include:
- Reviewing and improving MFA and Conditional Access
- Removing or minimising legacy authentication
- Deploying and managing Microsoft Defender
- Designing and implementing Intune device management
- Setting up Microsoft 365 backup and recovery
- Using Secure Score as a continuous improvement guide
We can help as:
- A fully managed IT & security partner, or
- A co-managed Microsoft cloud specialist alongside your existing IT team.
Ready to Fix These Microsoft 365 Security Mistakes?
If your business lives in Microsoft 365 and some of the issues in this article sound uncomfortably familiar, now is the time to act – ideally before you’re dealing with a real breach or data loss incident.
Next steps:
👉 Explore our Cyber Security & Microsoft 365 Compliance services
👉 Learn how we protect data on the Microsoft 365 Backup & Disaster Recovery page
👉 Or book a Security & Compliance Assessment via our Contact page
So your team can keep working the way they want – and you can Bee Secure, Bee Connected, Bee Confident that Microsoft 365 is actually locked down properly.
