Office 365 Migration Plan 1

Office 365 Migration Plan: Part 1 – Preparation

Chay Douglas Data Migration, Microsoft Exchange, Office 365

The secret to a successful migration is all in the planning. Here we discuss best practices of an Office 365 Migration Plan.

Determine the Scope of Migration

Before we begin doing anything, we have to determine what needs migrating and what can be cleaned up. While we need to make sure everything we need is available in the target, we can use this time to ensure that unwanted data isn’t migrated, taking up unnecessary licenses and slowing the migration down.

So, we need to ask if the following are necessary for your Office 365 Migration:

  • All Mailboxes
  • Leaver Mailboxes
  • Service accounts
  • Shared mailboxes

Once the essential data has been determined, is it worth cleaning up or organising the remaining data as to save storage and remove the risk of error? Or can this excess data just be ignored until the migrating is completed and then decommissioned as a whole?

Decisions must be made to ensure the optimum performance of the migration, required data is available upon completion and/or any quick storage wins can be gained.

Active Directory Consideration

The first Active Directory consideration to be made it whether to keep an on-premise version or migrate it to the Cloud.

There are two ways to deal with Active Directory when migrating mailboxes to Office 365:

  1. Migrate Active Directory to Office 365
  2. Synchronise Active Directory

By Migrating AD to Office 365, all admin work is completed in the cloud with AD and Mailbox management removed entirely from on-premise. This is the expected and most utilised way of migrating to Office 365. We are moving to the cloud for a reason, right? To remove on-premise overheads…

However, there are ways of keeping the on-premise AD and integrating with the Mailboxes on O365. Utilising this type of integration, the on-premise AD is replicated to Office 365 but can be administered from both on-premise or in Office 365. Any changes made on either end, are replicated ensuring both versions of AD are consistently the same.

There are 2 ways of connecting to the AD when choosing to synchronise between on-premise and the cloud. One is to provide a username and password to each of the on premise and O365 accounts. Even with password synchronisation between the two account, the user will be required to sign in to each version of AD separately. The other is by using Single Sign-On (SSO) which allows the on-premise account to log into the Office 365 account. For more information on this, please refer to the technote: Office 365 integration with on-premises environments

How you chose to deal with Active Directory is up to preference. Are the IT team ready for the wholesale change or would they prefer to keep an on-premise version? Does it make more sense to just reclaim the on-premise space and outsource it to the cloud?

The second consideration is to determine if any AD consolidation can be completed before the Office 365 migration.

If your environment is one with multiple forests and domains, is it possible to consolidate these ready for a 1-to-1 migration?

By consolidating your Active Directory can provide a number of benefits:

  • Centralised management and monitoring
  • Fewer Domain Controllers to maintain and migrate
  • Easier troubleshooting
  • Fewer GPO inconsistencies
  • Easier migration/integration to the cloud
  • Easier to future manage

For a balanced and more detailed view of advantages and disadvantages of AD consolidation, please see Part 2 of this Active Directory Migration Considerations Tutorial with further details on how to go about consolidating in the complete tutorial on, over 8 parts.

Which O365 Features Will Be Utilised

Along with the decision Active Directory, there are many decisions in which features in Office 365 will be utilised and which users will be granted access to them.

Not only are features essential for selecting the right Licensing Plan, but coming up with planned policies for which features are made available and to who is something worth considering as part of the Office 365 migration.

Office 365 office the Full Office Application Suite, as well as a selection of services along with Exchange and Active Directory, including:

  • Lync
  • Yammer
  • SharePoint
  • Exchange Online Archiving
  • eDiscovery

The business decision should be made as to which features are required and therefore which Plan is selected as well as which subsets of users are allowed access to these features.

Retention Policies

There are many considerations in and around the retention periods of data within any business. Before migrating to Office 365 without implementing any retention policies there are a number of questions to ask:

  • Are there legal requirements with data in your business?
  • Are items staying longer than they should be?
  • Do retention policies need to be created and implemented after the migration?
  • Are there currently any retention policies in place?
  • Do existing retention policies need to be replicated?
  • Can items stay forever?
  • Can items older than required be removed before the migration?

9 out of 10 times, retention policies will be forced due to legal requirements, but perhaps just in-house policies suggests data older than a certain age is to be purged. These considerations will have to be assessed before implementation on Office 365.

By removing any excess data, not only will it be legally compliant but ensure a faster migration.


As Microsoft Exchange is a heavily capacity intensive application, there is always a need to ensure that it doesn’t grow out of hand with the sheer number of calls and mass amounts of data. As such, it is common practise to implementing an Archiving solutions to archive items of a certain age or quota to cheaper, less intensive storage.

As such, this archived data is often just as important as the existing Microsoft Exchange data and will no doubt require migrating to Office 365 as part of the mailbox migration.

There are a number of considerations around archived data:

  • How easy is the native migration out of the archiving solution?
  • Would a 3rd Party tool be more suited in order to migrate the archived data, for speed and assurance due to chain-of-custody and the mitigation against human-error?
  • Can the migrated users be given access to the on-premise archived data while the migration is completed?
  • Can archived data be sorted and any unnecessary data be removed or decommissioned?
  • Can the archived data be migrated before the mailbox migration and therefore ready for the user when the Mailboxes are migrated?

Another thing to consider while migrating the archives is if the Office 365 environment has Exchange Online Archives (EOA) enabled. If so, would it be beneficial to migrate the archived items to this depository rather than the Office 365 primary mailbox in order to keep it lean, yet still providing access to the archived data.

Disaster Recovery Planning

Nobody likes to think it’ll happen to them, but no project ever goes ahead, and rightly so, without a plan if the proverbial feces hits the rotary blade.

With an Office 365 migration there are a number of potential points needed for recovery:

  • Active Directory. Ensure that there is a line-in-the-sand in order to roll back to before undertaking the project and editing the directory
  • Exchange Servers. Snapshots and point-in-time recoveries are always handy, but always ensure that any migrated messages to Office 365 have been migrated back accordingly.
  • Archives. Any archive changes will require a recovery model here even if the migration is a pure copy. Ensure that the integration after a recovery is not lost to the on-premise Exchange.
  • 3rd Party. Any third-party tools or companies require roll-back procedures in place and if they do not provide one or provide something unviable it’s best to avoid these like the plague!

Existing Infrastructure

As Office 365 is provided with consistent up-times, all network impacts during the migration will be provided by your organisation environment.

Bandwidth tests are a good place to start with determining the upload and download times you are reaching in order to estimate the expected timescale of the project.

Carrying out these tests before the migration not only helps provide an expected timescale and mitigates against any surprises during the migration, it can be used to determine which calls are particularly heavy on the network and can go someway to clearing up the bandwidth.

Once nuisance applications are sorted and removed from adding to the network traffic, the network usage can be assessed in order to draw up optimum times in order to possibly schedule the Office 365 migration.

Prepare the Organisation

In order for any project to run as smoothly as it should, not just from the IT side, but for the end-user and business partners as well, the key to success is always in being prepared and planning efficiently.

Create a checklist

As mentioned previously, there are a number of considerations that need to be addressed before undertaking the project. To ensure all of these are met and every relevant user is aware, a checklist is a simple and efficient way of ensuring all things are considered and reviewed.

Reporting and Management

By carrying out reporting against licenses, inactive accounts and the number of live users. Decisions can be made to ensure that excess licenses are not applied and only the requisite information is migrated and kept where needed.

Password Management

Password management is also key to all stages of the project. There is no doubt during the migration, users will get confused by the change of environments and the first calls to helpdesks will be password and username related. It is vital that there is a procedure to deal with such calls from both on-premise and Office 365 queries.


I cannot stress enough just how important this is. We have seen many customer projects become derailed due to poor documentation. Where team members happen to leave the project before completing or simply a delay in the project elsewhere, for a new user to come in and/or a project to be continued a year later, it is increasingly made more difficult by poor documentation.

If each step along the way is documented, with, even just an outline of, how steps were completed and which factors were the cause of some decisions made, it makes to project seriously easier for all involved.

Formalise Milestones

As part of the documentation, Milestones along the project should be drawn up and documented each time one is met and how it was met.


By documenting, each party involved from the IT team, 3rd Parties, end-users and, perhaps most importantly, the directors are made aware of where the project is at any stage. Miscommunication is often the biggest thorn in a project’s side that really complicate matters a lot more than necessary.

Along with all parties being aware, documenting in such a way leads to the reducing of potential risks and improving consistency throughout the Office 365 migration.

By failing to prepare, you are preparing to fail – Benjamin Franklin

Thank you for reading this 1st of a 3 part blog on an Office 365 Migration – Planning.

Office 365 Migration Plan – Part 2: Implementation now available

At MirrorSphere, we are experts in email migration and we’re happy to talk you through your Office 365 Migration options.

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