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How to Consolidate Active Directory, Exchange, and Office 365 After Merger

Day One of your merger or acquisition is in the books. You pushed hard to integrate your identity and messaging so that your users could start collaborating right out of the gate. You’ve set things up so that users can look each other up in a shared directory, send emails back and forth, schedule meetings, and more.

How to Consolidate Active Directory, Exchange, and Office 365 After Merger

How to Consolidate Active Directory, Exchange, and Office 365 After Merger

Now, you’ve got a bit more breathing room to consolidate everyone onto the same platform. And you need to do it without disrupting your users. In this article, we walk you through what that process looks like. Specifically, we share considerations and best practices for how to:

  • Consolidate Active Directory
  • Consolidate on-premises Microsoft Exchange
  • Consolidate Microsoft Office 365
  • Support end-users after the migration

Table of contents

A Common M&A Scenario
Planning Your Migration
Get ready to collaborate by Day One
Merging identities, users and systems after Day One
Migrate Identities to a Unified Active Directory
Key challenges of Active Directory migrations
Sequencing your Active Directory migration
Choosing the right Active Directory migration software
Consolidating Messaging into Exchange or Office 365
Key challenges of Exchange migrations
Sequencing your Exchange migration
Choosing the right Exchange migration software
Consolidating Office 365 Tenants
Key challenges of Office 365 tenant-to-tenant migrations
Sequencing the Office 365 cross-tenant migration
Choosing the right Office 365 cross-tenant migration software
Supporting End-Users After the Migration

A Common M&A Scenario

First, let’s set the stage. When we talk about consolidating IT after a merger, there are many different scenarios and products we could cover. But in this white paper, we focus on the most common scenario we see with our clients. This is where a company uses Active Directory as its primary directory to manage identity. Then for their messaging, they use Microsoft Exchange, whether that’s Exchange on-premises, Exchange Online in Office 365, or a hybrid of the two.

We will also focus on M&A projects within larger enterprises (2,500+ users) in this paper. That’s because enterprise migration projects are often more complex than projects for small or medium-sized businesses (500 users or less). With these smaller projects, you’re often able to migrate the identities and email data in days or even a week. But enterprise projects can take much longer and have more requirements due to the size and complexity of the project.

Planning Your Migration

If you don’t have a plan, then you plan to fail. This is especially true in mergers and acquisitions, where there are a lot of moving pieces, an aggressive timeline, and a slew of new colleagues to start collaborating with. So, these projects take significant planning to make sure you have all your ducks in a row before you get into the actual IT infrastructure changes that will happen as part of the merger. Here are the two high-level phases for mergers:

Get ready to collaborate by Day One

The first goal is to make it easy for your users to collaborate on Day One. Given your average merger timeline, you probably won’t have had a chance by that point to migrate everyone onto the same platform. So, your goal for day one is to set up a connector between the companies. You have them co-exist for a while as you work on the broader migration after Day One.

By Day One, your users should be able to:

  • Look up contacts in a unified directory
  • Send and receive email
  • Schedule and update meetings
  • Share a unified email address
Get ready to collaborate by Day One

Get ready to collaborate by Day One

Merging identities, users and systems after Day One

After you set up coexistence for Day One, you can now start to plan and prepare to consolidate the IT environments. This is where you merge identities, mail, and other data into a unified environment. You might need to migrate mailboxes, public folders, or workloads like SharePoint and OneDrive for Business. Depending on how many users you have, the amount of data that needs to be moved, the complexity of your systems, the bandwidth available on your network and a variety of other factors, this phase of the project can take anywhere from a few weeks to many months.

There’s a lot to do to get ready for this phase. There are aspects of your environment that you will need to analyze and remediate that you didn’t need to address to enable collaboration on Day One. You’ll need to assess the users and their workstations to find out how much data they have, what software and versions they use, what their work schedules are like, and who their teammates and delegates are. Plus, you’ll need to ensure your source and target environments are ready to support the transition of users, servers, workstations, and applications between the platforms.

This is the meat of what we cover in this white paper. In the coming sections, we share best practices for how to:

  • Migrate identities to a unified Active Directory environment
  • Migrate mail to a unified messaging environment
  • Migrate public folders to a unified environment
  • Migrate other workloads to a unified environment
Merging identities, users and systems after Day One

Merging identities, users and systems after Day One

Migrate Identities to a Unified Active Directory

The first step is to consolidate Active Directory. You need to set up a single, unified directory that serves as your identity platform. It supports everything else that you’ll be migrating, including your messaging and other applications. You’ll need this foundation in place whether you’re migrating on-premises, to the cloud, or a mix of both.

Here are the key challenges to be aware of in this type of migration, suggested steps to take, and what to look for in your migration software.

Key challenges of Active Directory migrations

When it comes to merging Active Directory, there are some key challenges to consider:

User impact. When you start to move users from one domain to another, it could easily impact their workflow. Every day, people log in to their laptops, to the network, to their email and other applications. The moment they try to log on, there’s a potential impact. If something goes wrong in your migration, this is the point at which users will notice. They won’t be able to access their resources. And your help desk calls could go through the roof.

Migrating in the absence of trust. In mergers, you’re often not able to set up a trust between the two organizations before you migrate. How do you migrate in the absence of trust? Some migration tools don’t support this.

Migrating without shared admin access. Typically, companies won’t have shared admin access before the merger. And even after Day One, you still might not have capabilities there. You have two different IT staffs, so you may not have that shared admin access between the two different systems you’re migrating between. This can pose a challenge.

Dealing with a distributed network. Maybe you have to migrate a distributed network. You might have people who are offline, who are working from home, who are travelling, who are at customer sites. How do you deal with moving that device, that person, into a new domain when they’re not connected all the time?

Updating access. You need people to get access to the right pieces of information at the right time with the right credentials. So, you need to make sure that you’re preserving Access Control Lists (ACLs) appropriately as you move someone from one domain to another.

Sequencing your Active Directory migration

We recommend four key phases for Active Directory migrations and consolidations:


  • Planning and design
  • Find and fix issues upfront
  • Set up interoperability between environments

Move the back end:

  • AD users, groups, other objects and their properties
  • Align to plan
  • Object mapping, matching, and creation nuances

Move the front end:

  • Prepare devices
  • Re-ACL servers and workstations
  • Cut devices over to the new environment

Move applications:

  • Explore app migration considerations
  • Migrate standard Microsoft apps
  • Migrate third-party apps

Choosing the right Active Directory migration software

You have many options for scripts and software that can help you migrate Active Directory. These range from free tools from Microsoft to DIY scripts to a range of third-party software. Depending on the complexity of your migration, you’ll find that some of these options work better than others. So, it’s important to choose the most robust and flexible solution to meet your needs. Look for migration software that:

Migrates without a trust. Trusts are useful, but they can be difficult to implement. And it might not be possible for you to set up a trust in the context of your merger. Sometimes industry regulations prevent you from doing that. So, if you don’t need to (or can’t) set up a trust, why should your software require it? Keep it simple and look for a solution where you can migrate without trust.

Keeps your data secure. This is a huge one to watch out for, as many migration tools rely on legacy protocols that punch thousands of new holes in your firewall. In fact, some tools out there require as many as 60,000 open ports, which is a big security risk. So, you should choose software that doesn’t require remote procedure calls or remote registry access. Again, keep it as simple as possible because simplicity makes for a better security platform.

Enables you to customize the synchronization. Your migration software should be flexible enough to let you set up the sync however you need. For example, you might want to set the sync to run at a custom interval, whether that’s every 30 seconds or every 30 minutes.

Enables you to customize how you migrate objects. Migration is a great time to standardize and clean up your Active Directory objects. So, as you migrate, you might need to re-map attributes. You might want to take an attribute from an existing object and populate it into some other place in the new Active Directory environment. Or you might want to re-name an attribute. So, it’s important to choose a tool that lets you modify those object attributes as you migrate.

Migrates remote workstations. People who work remotely aren’t always logged on to the domain. And it’s sometimes not feasible for them to come into the office. So how do you get those people over to the new domain? Your software should be able to cache credentials and then do an offline domain join. And it should do this for you automatically, without you or your users having to take any action.

Helps you manage the project. Finally, you want a product that’s easy to use. It shouldn’t require you to write custom scripts. It should let you do dry-run tests so you can see what’s going to happen before you make it happen. And it should have ample tracking and reporting to let you know the status at every step.

Consolidating Messaging into Exchange or Office 365

After you’re well on your way to consolidating your directories, you should turn to consolidate your messaging environments. We’ll focus on best practices for migrating between on-premises Exchange environments or migrating mail and end-users from Exchange on-premises to Exchange Online in Office 365.

While these are relatively straightforward moves, there are still some things to watch out for here. These are the key challenges to be aware of in this type of migration, suggested phases, and what to look for in your migration software.

Key challenges of Exchange migrations

There are some key challenges to consider for Exchange migrations:

Analysis of content. Most companies don’t migrate their data as-is. By doing that, you can waste time and effort bringing over data that you no longer need. So, part of the effort here is to take a look at what you’ve got. How much content do you have? How much do you really need to move? Can you archive or delete some of it? It can be a challenge to do this analysis and get buy-in to make these decisions.

End-user experience. This is an important piece to consider upfront. If you’re not getting this right, then your users can get disgruntled. This can reflect poorly on your migration project, and then the migration will start to fall apart. We’ve seen this happen more than once from not factoring in issues like end-user work schedules, mailbox delegation, and more. So, it’s really important that you maintain a positive end-user experience throughout the migration. In a perfect world, they shouldn’t even notice that you’re migrating.

Environment readiness. Is the legacy environment ready to be moved? Do you have a new environment set up? Are you moving from on-premises to the cloud? Are you prepared to do that, with licenses in place?

Custom requirements. Do you have any custom requirements for how you’re going to move your mail? Maybe you’ve decided you’re going to implement new mail quotas in the new environment, where you didn’t have any before. So, what will happen to any mail attachments that exceed this quota?

Scheduling and forecasting. It can be a challenge to figure out how long your migration might take. This depends on many factors, like the amount of data you’re moving and how fast your network is. So, you want to try to estimate, at a granular level, how long it’s going to take to move a mailbox from one place to another.

Synchronization with related processes. Usually, in these sorts of mergers, there are a lot of moving parts, so you need to make sure that your Exchange migration fits in with the rest of the conga line. You need to stay plugged into the status of all your migration projects and make sure that you don’t do something that’s going to cause something else to break.

Sequencing your Exchange migration

Here are the phases we recommend for an on-premises Exchange migration.

Plan and prepare

  • Planning & Design
  • Analyze your environment
  • Fix any issues

Establish coexistence:

  • Directory
  • Availability
  • Messaging
  • Calendar
  • Applications

Move users:

  • Continuity of interoperability
  • Scheduling and forecasting
  • Notify users
  • Track and report

Move data:

  • Migrate mailboxes
  • Archive or remove old mailboxes
  • Migrate public folders

Choosing the right Exchange migration software

Again, you have many options for scripts and software that can help you migrate between Exchange environments. But depending on the complexity of your migration, you’ll find that some of these options work better than others, especially for meeting the requirements of larger migration projects. So, it’s important to choose the most robust and flexible solution to meet your needs. Look for software that lets you:

Synchronize directories. You need to make sure that people can find their new colleagues easily, by synchronizing directories to establish a unified Global Address List (GAL).

Communicate with end-users. Your software should help make it easier for you to keep users in the loop about what’s going on. You should notify them at several steps in the process: what’s about to happen, when it’s going to happen, how long you expect it to take, and when it’s actually done. You should also tell them where to go to get help if they have any issues.

Schedule and forecast accurately. The right software can help you properly schedule the migration and get an accurate representation of how long the entire project could take. The software should help you to set up an efficient migration schedule by letting you filter mailbox and Active Directory attributes as well as set up migration groups and blackout windows. It should also help you to perform dry-runs or pilots to gauge your migration throughput and generate a reliable forecast for the completion of your migration.

Enterprise scalability and throughput. Typically, mail systems have a lot of data. Organizations often essentially use it as a file store. Even though people are starting to go to other communication platforms, mail seems to be the bedrock of almost all communications within corporations. So, the software you choose should help you move content as quickly as possible, and at the scale you need.

Manage the project from end to end. As an admin, you need to follow along with what’s happening, how fast you’re moving, and whether you’re on schedule. So, your software should give you an easy interface to track how your migration is going.

Synchronize and migrate public folders. Even though Microsoft has been trying to phase out public folders for a decade now, they’re still prevalent. If your organization still uses them, you need to capture that data and move it to a new location in the new environment.

Consolidating Office 365 Tenants

The last scenario we’ll talk about is when you need to consolidate two or more environments within Office 365. This is a bit different than a migration within an on-premises Exchange scenario. Unlike on-premises, you don’t control the environment. Microsoft does. You’re letting Microsoft take care of the environment for you, for many good reasons. But it does mean some different considerations when you think about an Office 365 migration.

Here are the key challenges to be aware of in this type of migration, suggested phases, and what to look for in your migration software.

Key challenges of Office 365 tenant-to-tenant migrations

There are some unique challenges that come with merging tenants of Office 365. That’s because Microsoft designed the platform in such that way that it can be a challenge to link tenants and have them work as a single entity. In fact, you can’t do it out of the box. Here are some of the challenges you’ll face in this scenario:

Sharing a unified email domain. One of your goals in your merger is likely to unify under the same brand. That means you’ll likely want to share email domains and addresses. But out of the box, you can’t share a single email domain between tenants of Office 365.

Integrating GALs and calendars between tenants. This is another thing that you can’t do natively in Office 365. There’s no out of the box way to integrate the global address lists and calendars between different tenants.

No free tools from Microsoft. As of the writing of this paper, Microsoft doesn’t offer any free tools to help with tenant-to-tenant migrations. And there’s no way to go to Microsoft and say “We’re merging, we need you to grab this tenant and then drop it into the other one.” So, you’ll need to look at paid software or scripting.

Manually disabling old mailboxes. There’s no way to automatically disable old mailboxes after you’ve migrated them. Instead, you have to do this manually. Even if you’re successful through some scripting process or some other tool that you may have written to be able to move mailboxes, you still then have to go back and disable the old ones.

Required downtime. Natively within Office 365, downtime is required to switch the domain from source to target. So, your mail servers will be offline during that cutover. And because it’s a cloud environment, you don’t have control over how long that downtime might be. It could be 30 minutes. It could be 3 hours or longer. So, this is something to plan carefully.

Migrating other workloads. Some workloads in Office 365 are difficult to migrate or can’t be migrated at all. Take SharePoint, for example. How do you migrate content from one SharePoint site to another? This isn’t always a straightforward task. So, if you need to migrate content from other workloads of Office 365, this can add complexity to your migration.

Sequencing the Office 365 cross-tenant migration

Here are the four key phases in an Office 365 tenant-to-tenant migration:

Plan and prepare:

  • Plan the consolidated tenant
  • Analyze your content

Integrate tenants:

  • Unify email domains
  • Unify GALs
  • Unify mail flow
  • Unify calendar lookups
  • Sync public folders

Move mail:

  • Migrate mailboxes
  • Direct Outlook profiles to new mailboxes
  • Disable old mailboxes
  • Migrate public folders

Move other workloads:

  • Skype for Business
  • SharePoint
  • OneDrive for Business
  • …and more

Choosing the right Office 365 cross-tenant migration software

Given the challenges of migrating between tenants of Office 365, the right migration software can really make or break these projects. Your migration software should:

Unify email domains. The software you choose should have the capability to unify your email domains and addresses. So, from Day One, you’re able to present yourself to the outside world as a unified brand.

Unify the GALs. The software should also make it easy for people to look up their new colleagues in a unified Global Address List. And it needs to keep these lists in sync over time as you migrate.

Unify the calendar lookups. Calendar is one of the key applications that come into play in a merger. That’s because it’s often the first point of collaboration. People want to start setting up meetings with their new colleagues. But to do that, they need to able to see when people are free. So, the software you choose should allow people to see free/busy information.

Migrate mail at high speeds. You essentially have unlimited storage through Office 365, whether through archive storage or through your mailbox. So, there’s often a lot of content stored in there. Which means you need to be able to handle moving that content from one place to another, at high velocity.

Move the domain without downtime. The software you choose should be able to move the domain without downtime or interrupting the productivity and collaboration of your end-users.

Sync and migrate public folders. Public folders are still out there, even in Office 365. So, you’ll need to be able to grab information at the cloud level and move it from one tenant to another.

Migrate other Office 365 workloads. Finally, you need to consider any other workloads in Office 365, like Skype, SharePoint, OneDrive, and Yammer. If you have content stored in those workloads, you’ll need to plan how you’ll move it over.

Supporting End-Users After the Migration

Last up, we wanted to devote a special section to a crucial and oft-neglected step in the migration process. When you’re in the throes of an M&A and everything is moving quickly, it can be easy to skimp on the softer side of this project—user training and onboarding.

IT teams are often too heads down on the migration itself to focus on this piece. Or maybe they don’t have the skills (or interest) in-house to drive effective onboarding. But you need to keep in mind that in many M&A scenarios some, or perhaps all, of your end-users are being moved to an email and collaboration environment that is different from the one they used prior.

“End user IT training is often overlooked or underfunded, which becomes particularly evident during M&A events.” – Gartner

It’s not enough merely to move your users to a new platform. You need to inspire them to use it. This is especially true if the users are new to Office 365, where there are a lot of new features and workloads that users might not be familiar with.

Here are four key strategies you can use to help onboard users quickly and effectively:

End-user adoption campaigns. Before, during, and after your migration, you need to be communicating with users about what’s coming—and how it will benefit them. You need to start educating them about the capabilities of the new software, and how features might differ a bit from what they’re used to.

Instructor-led training. These types of training events are great to help users learn about how the new platform will make their lives easier. Or even do a deep-dive comparison of how something worked in the old platform versus the new. People can bring their questions and get hands-on demos of key features or new workloads they need to be aware of.

On-demand learning resources. Some users prefer to learn at their own pace. So, an important supplement to any live training is a library of on-demand learning resources. Users should be able to go out and look at a video, read a how-to article, or get a quick tip for how to do something in the new world.

Enhanced help desk capabilities. Your in-house help desk might not have the capabilities or scale to support a slew of user questions about the new software. You should consider augmenting your help desk with an expanded help desk focused on end-user adoption.


Those are the key things to think about when it comes to consolidating Active Directory, Exchange, and Office 365 after a merger. As we’ve shown, you need to plan carefully to sidestep some of the common challenges that come with these types of projects. To ease the transformation, you should sequence the project correctly and choose the right software and services to help automate your migration. And don’t forget your user onboarding and training. By doing all of these things in concert, you’ll be well on your way to an effective transformation —and setting yourself up for a more productive merger.

Source: Binary Tree

Alex Lim is a certified IT Technical Support Architect with over 15 years of experience in designing, implementing, and troubleshooting complex IT systems and networks. He has worked for leading IT companies, such as Microsoft, IBM, and Cisco, providing technical support and solutions to clients across various industries and sectors. Alex has a bachelor’s degree in computer science from the National University of Singapore and a master’s degree in information security from the Massachusetts Institute of Technology. He is also the author of several best-selling books on IT technical support, such as The IT Technical Support Handbook and Troubleshooting IT Systems and Networks. Alex lives in Bandar, Johore, Malaysia with his wife and two chilrdren. You can reach him at [email protected] or follow him on Website | Twitter | Facebook

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