01 Jul Microsoft 365 Security: A Post-Migration Checklist for Australian SMBs
Microsoft 365 security often stalls the moment a migration finishes. The mailboxes and files move across, everyone can log in, and the project gets signed off, but the security controls that come with the licence are left at their default settings. That leaves exposure sitting unmanaged and a business paying for protections nobody has switched on.
This checklist covers the configurations worth confirming once the migration is done, from sign-in controls to sharing and monitoring. It builds on the broader picture in The Complete Guide to Microsoft 365 Consulting for Businesses, then narrows in on the security settings that matter most day to day.
Why Microsoft 365 Security Slips After Migration
Most businesses treat the migration as the finish line. Once the mailboxes and files are across and people can work, the project closes and the default tenant settings, the baseline configuration Microsoft applies, stay exactly as they were.
That is how a Microsoft 365 post migration environment ends up with unmanaged accounts, open sharing, and no monitoring. Leaving the tenant ungoverned is one of the more common Microsoft 365 Security Risks for SMBs, because the exposure is invisible until something goes wrong.
Microsoft 365 compliance is the other reason default settings matter. Under the Privacy Act, and any industry-specific rules for your sector, the obligation to take reasonable steps to protect personal information sits with your business, as the OAIC sets out in APP 11. The licence gives you tools that support those steps, but only once they are configured.
The Post-Migration Security Configurations Worth Checking First
Think of this as your M365 security checklist: the configurations to confirm before assuming the environment is secure. Each one is included in most business licences and sits within a wider, layered approach to Cyber Security Services.
Turn On Multi-Factor Authentication
Multi-factor authentication (MFA) asks for a second check at sign-in, usually a prompt on a phone, on top of the password. It should be enforced for every user, with administrators first because their accounts carry the most access.
Treat MFA as a baseline expectation rather than an optional extra. It sits within the ASD Essential Eight, the Australian Government’s baseline set of mitigation strategies for internet-connected networks.
Set Conditional Access Policies
Conditional Access is a set of rules that decide who can sign in, from where, and on what device before access is granted. The policies weigh signals such as the user, their device, and their location, then apply the right control.
Microsoft describes how these signals combine in its Conditional Access documentation. A few sensible rules reduce the chance of a stolen password being used from an unexpected location.
Harden Email Against Phishing and Spam
Email is where most attacks start, and Microsoft 365 ships with anti-phishing, anti-spam, and safe attachment settings that still need configuring after migration. Turning these on and tuning them to how your team works closes gaps that default settings leave open. There are practical steps to Enhance Your Email Security that tighten the mail environment.
Apply Data Loss Prevention for Compliance Sectors
Data loss prevention (DLP) is a set of rules that identify and monitor sensitive information, such as financial records or personal data, and help stop it leaving the environment. It matters most for regulated sectors, where the movement of that information carries real obligations. Microsoft explains how DLP policies identify and monitor sensitive content across services like Exchange and SharePoint.
SharePoint and OneDrive Need Governance to Stay Secure
Migration often leaves sharing wide open. Default settings can allow files and sites to be shared broadly, including with people outside the business, so SharePoint governance starts with tightening sharing policies and external access controls. Reviewing these is one of the M365 Settings Worth Checking once the migration is done, before staff build new sites on top of loose defaults.
A short list of controls worth confirming:
- External sharing controls, so files leave the business only when intended
- Retention policies, so content is kept or removed in line with your obligations
- Version control, so earlier versions of documents can be recovered
- Guest access review, so external accounts are removed when no longer needed
Governance is ongoing work. As staff create sites and share files, permissions spread and access that made sense last quarter can quietly become a problem. A regular review keeps the environment matched to how the business actually works.
Keep Security Working After the Configuration
Configuration is the start, and visibility is what keeps it honest. Microsoft Secure Score gives you a measure of your current settings and a list of recommended actions, while the audit logs record what is actually happening in the tenant.
Acting on what they surface is what improves security over time. Pairing the numbers with regular reporting turns a static score into something your team can act on.
The other half is a steady maintenance rhythm. A quarterly review keeps settings aligned as staff, devices, and needs change.
It also helps to have a basic incident response plan, so the business knows who does what if something goes wrong. Neither has to be complicated, but both need to exist before they are needed.
The Gaps Most Teams Miss After Migration
Most gaps are not exotic. They are controls left switched off or processes that were never set up, usually quick to fix once someone looks. These are the ones worth checking first:
- MFA not enforced for every user, so some accounts still rely on a password alone
- Legacy authentication still enabled, which lets older sign-in methods bypass modern controls
- External sharing left unrestricted, so files can leave the business without anyone noticing
- No offboarding process, so accounts for departed staff stay active
- No one reviewing security alerts, so warnings go unread until an issue becomes an incident
Where to Start
Start by confirming which of these controls are already on and which are still sitting at their default. A short audit of MFA, Conditional Access, email settings, sharing, and monitoring shows what the migration left in place and what still needs attention.
If your team needs stronger security, better visibility, or a more structured post-migration setup, TCT can review your current tenant through Microsoft 365 Consulting and recommend what fits.
Frequently Asked Questions
What should be my first Microsoft 365 security step after migration?
Enforce multi-factor authentication for every user. It is the highest-value first move, and administrators should be covered first because their accounts carry the most access.
Does Microsoft 365 compliance cover Australian Privacy Act obligations automatically?
No. The tools support your obligations, but the responsibility sits with your business. Configuration and governance are what make the environment compliant, not the licence alone.
How does Conditional Access improve day-to-day security?
Conditional Access controls who signs in, from where, and on what device. That reduces the risk of stolen credentials being used from an unmanaged location.
How often should we review SharePoint governance and sharing settings?
A quarterly review works well for most businesses. Sharing and permissions spread as staff create and share content, so regular checks keep access matched to need.