IT Due Diligence Checklist for Microsoft 365 Mergers

Merging two companies means merging two Microsoft 365 tenants. And that is rarely as simple as pointing one at the other. Every successful merger comes with a properly planned due diligence checklist. Skip the due diligence steps, and you are likely to face broken permissions, missing Teams chats, compliance gaps, or something more unexpected like massive financial loss or tragic legal lawsuits.

Why Every Microsoft 365 Merger Needs a Plan First

Treating
Microsoft 365 data as just simple emails during a merger or acquisition can
cost a heavy penalty to your business. What you are merging is your years of
important emails, documents, chats, and more stored across various Microsoft
365 services. Skip the planning, and here's roughly what you will face:

• Identity controls

• Tenant health

• Compliance gaps

• Licensing optimization

• Technical debt

• Admin retention

• Active litigation holds

• Throttling & migration costs

• App and API integrations

• Business continuity planning

• SharePoint sites inaccessibility

• Broken permissions

• Delayed email delivery

The IT Due Diligence Checklist: What Needs to be Done Before

Office 365 stores data across multiple services such as SharePoint Online, Teams, OneDrive, Exchange Online, etc. And if you don’t analyze the data stored inside them correctly, then you might run into some major losses. Here is what actually needs to be reviewed before merging two Microsoft tenants:

Document Entire Microsoft 365 Environments

You can’t plan a migration around data you don’t know exists. Start by recording everything you have in both of your Microsoft 365 tenants. Make sure to collect information about total users, guest users, Teams, SharePoint sites, OneDrive accounts, Shared mailboxes, distribution lists, Microsoft 365 Groups, etc.

Check Identity & Security Setup

Microsoft Entra ID is where most of the mergers & acquisitions get messy first. Look for duplicate UPNs, conflicting domains between both tenants, overlapping SMTP addresses, differences in MFA adoption, Conditional Access Policies, Self-Service Password Reset, etc.

Confirm Domain Ownership

Verify accepted domains, DNS ownership, and SPF, DKIM, DMARC, and MX records for every Office 365 domain involved in the merger. Getting this wrong doesn't just cause any confusion, it can break email delivery and authentication in between the merger.

Validate Compliance Obligations

Check retention policies, active legal holds, eDiscovery cases, Microsoft Purview settings, audit logs, and DLP policies in both Microsoft 365 tenants. Anything under hold needs a proper plan before migration.

Audit Licensing

Duplicate subscriptions and license plans are very common in merger & acquisition scenarios. And they are the easiest costs to catch if someone actually looks.

Examine Storage & Migration Volume

Analyze Exchange, SharePoint, OneDrive, and Teams file storage across both Microsoft 365 environments to prevent disruptions during merger.

Document all the Risks

Gather all the risks such as duplicate user identities, failed logins, domain conflicts, email disturbance, missing licenses, service interruption, broken permissions, unauthorized access, etc. and create a list.

Mistakes Worth Avoiding During Microsoft 365 Merger

Neglecting due diligence checklists can create many data blunders which can’t be reversed if gone too far. Here are some common mistakes which users should avoid while going under merger:

• Rushing discovery audit

• Ignoring additional applications

• No data backup strategy

• Identity management gaps

• MFA and policy misalignment

• Orphaned permissions

• Mismatched security baselines

• Ignoring throttling and limits

• Poor end-user communication

• Misunderstanding license rules

• Inadequate post-migration training

Last Say

Microsoft 365 acquisition & merger isn’t just about moving data from one tenant to another, its identity, security, compliance, and licensing exercise that happens alongside. And without a proper due diligence checklist, your migration would become challenging and chaotic. The checklist tells you what needs to move and what risks to plan for. Run the checklist first, and moving the data itself ends up being the easiest part of the entire process.