Let's assume that you are starting the process of planning your Exchange Online migration. In the article below we will discuss the components of managing a successful migration project. With the right approach and involving experienced specialists in the project (such as ours, at Fanetech), your company can take full advantage of the cloud's competitive advantages in terms of security, scalability and cost.

Exchange Online migration errors

As with any process, when carrying out a large number of migrations, it is easy to identify the errors that you encounter most often in migration projects. We have highlighted the following:


It is recommended to schedule the final stages of the migration over the weekend. It is optimal to schedule during non-working hours so as not to interrupt work processes. On Monday, when users return to work, most of the work will have been completed. Of course, users will have questions; to quickly resolve them, they need an effective technical support service that will be able to cope with the influx of requests.


Constant communication with end users must be of utmost importance. They must be informed in a timely manner about the stages of migration and the benefits it will bring.  With proper planning, support staff will have answers to frequently asked questions and solutions to common connection problems, such as new passwords and logins. It is recommended that your support team be trained to ensure they are fully prepared to handle as many incidents as possible so that you can complete the migration process as quickly as possible.



Many people assume that users need all the information they have to function effectively in their daily work. However, transferring all your data at once is not always achievable or necessary.

When users move to the cloud, they still have mailboxes, archives, files, and public folders. When you move between tenants, you add personal, group, and meeting chats to custom workloads, and you also add SharePoint, Teams, and Groups to shared workloads. All of these different workloads are unique and can add up to terabytes of data. The vast majority of this information is no longer relevant, is rarely accessed, and will likely not be needed within the next 90 days. These 90 days give you the opportunity to complete your migration and meet this tight deadline.

If you have a lot of data and little time to move it:

  • Provide each user with the last 90 days of data and then populate it with historical data.
  • Once the user moves and starts working in the new environment, you have time to migrate their entire archive while they continue to manage their daily workload.
  • By reducing the initial volume of data, it becomes possible to move your users faster.

Here's a surefire set of options to meet the end user's needs while keeping the original data size as small as possible.

  • Move over the last 90 days of mail, 90 days of meetings with all recurring meetings, personal contacts and tasks. These settings cover the contents of your user's mailbox.
  • Migrate recently used files and folders by date of use, minimize file versioning by migrating only the most recent versions, and filter out files that are too large or perhaps common file types such as media files that tend to weigh a lot.

These tips will help you connect your mailboxes to Exchange Online as quickly as possible. The strategy will remain the same for other types of migrations. Reduce the movement of initial data to get users to their destinations as quickly as possible, and then replenish their archived data.

As organizations increase their use of cloud storage, there may come a time when pre-migration of all your cloud data will become impractical. Adopting this type of strategy will be essential to successfully moving the vast amounts of data stored in today's environments. If you want to process large volumes of data in the shortest possible time, reduce the initial load by using file modification date filters, and then fill the archives over time. You will find that users remain productive and most of them don't know that some data has disappeared because they can see all the relevant files that they access most often.

Public folders

Public folders are a legacy technology that has been a part of Exchange since day one, and there are now endless more secure solutions to meet the same needs in Microsoft 365. Additionally, the same problems that caused organizations to move away from public folders still exist today. Public folders are uncontrollable, promote general sprawl, are difficult to regulate, and are difficult to motivate end users to adhere to retention and mailbox sizing policies when using public folders as an archiving solution. This was never what it was intended for.

Now that you've decided to move your on-premises mailboxes to the cloud, you need to decide where to move any public folder data you might still be storing. The benefit of moving to the cloud is that it gives you the opportunity to move data from shared folders to more modern collaboration tools such as  Office 365 Groups or even SharePoint Online. Of course, in Exchange Server 2013 and later, you have the option to go directly to Exchange Online public folders while maintaining the folder hierarchy and granular permission roles that public folders offer. However, there are some limitations that you should be aware of first. If any public folder in your organization is larger than 25 GB, Microsoft recommends clearing out unnecessary data to reduce the size (that is, deleting it if you don't need it), or first splitting the public folder's contents into multiple smaller public folders before migrating. Additionally, Exchange Online limits organization of public folder hierarchies to 500,000 public folders, and the maximum total size of all public folder mailboxes is 50 TB.

There are two reasonable migration paths: either keep the public folders on-premises (running in hybrid mode) because they exceed the Exchange Online limits, or migrate all the required public folder data to Office 365 groups. Each Office 365 group has a group mailbox with a maximum size 50GB, and groups offer many other benefits that shared folders don't. Convenience  Office 365 Groups is that in Outlook they can easily replace the email functionality that public folders previously offered to end users. In addition to the basic email functionality, there's a shared calendar where all team members can manage team meetings, collaborate on emails, documents, and even chat directly from the group. Another important difference between groups and shares that cannot be overstated is applications. When you move to a group, you unlock access to a vast library of powerful apps from Microsoft 365. Public folders don't offer integrations like this.

Why choose Office 365 over SharePoint Online? The process is simply simpler and was created specifically for this purpose. Using a batch migration managed using PowerShell or a third-party product will provide you with a method to copy mail and calendar data from public folders directly to Office 365 Groups without any intermediate steps. Moving the same data to SharePoint Online is not that easy. Additionally, once you've migrated shared folders to Office 365 Groups, you can convert those groups to Microsoft Teams if you want, offering your users even more collaboration solutions.


You must decide whether the applications are business critical enough to migrate. Each identified application must be assessed individually, which will result in some being removed and some remaining. If you decide to save, you must determine in what form they will be saved. Below are 5 application migration strategies to consider.

  1. Rehosting. Probably the most common application migration strategy is rehosting or migration. With this, you simply move your existing application to a cloud infrastructure as a service (IaaS) platform. This strategy is cost-effective and fast, but does not involve any modernization of the application (the application is still not cloud-based, so ongoing support must be considered).
  2. Correction.The next strategy is to revise the application. As you mature your application, you begin to change it to take advantage of cloud capabilities such as application containers and new data storage methods. This strategy aims to reduce operational costs through managed cloud services, but requires application and new technology experts to develop a plan to release them without interrupting existing services.
  3. Redesign. Where the last strategy might be considered a light application modification, the next strategy, in contrast, might be considered a major modification or redesign strategy. When you rebuild an application, you rely heavily on cloud capabilities to achieve your goals. As in with the latter, this strategy requires a plan and team to migrate the application smoothly.
  4. Recovery. If you are unable to review or change the application architecture, you may need to start over from rebuilding. A rebuild consists of discarding some or all of the existing code and starting over. This approach has many advantages if the application is truly important to your organization. With Microsoft 365 Power Apps and Dynamics, you may find that the rebuild may not require an experienced developer or team to plan the migration. Rebuilding can also give you the opportunity to simplify and improve the original application design.
  5. Replacement. The final application migration strategy is to simply replace them with something else. If you can find a SaaS provider for your custom application, then this strategy ensures low application implementation time. 

Preparing to move to the cloud

Many people are planning to migrate their mailboxes, archives, and public folders to Exchange Online. The tips above will help you understand what to do and what to avoid when planning your Exchange Online migration.

If you need help with your migration project, Fanetech can help you with planning and implementation. For advice, just contact us.

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