As more organizations move to Office 365 during mergers and acquisitions, they need robust solutions to consolidate their Office 365 infrastructure and services. This article explains how to migrate from Office 365 to Office 365 using a combination of Cloudiway products.

Features of the Cloudiway solution

Cloudiway provides a single solution for all the steps of your migration:

  • user and group provisioning;
  • OneDrive to OneDrive migration;
  • SharePoint Online to SharePoint Online migration; and,
  • mail migration including contacts and calendars; and,
  • coexistence solutions (mail routing, calendar free/busy, address book synchronisation).

Benefits of the Cloudiway solution

  • no storage of your mail, files or site data, so no security risk (migration takes place in memory only: we store only a unique ID per mail, file or site to ensure its migration status can be monitored);
  • secure, encrypted data transfer with no loss;
  • fast data throughput: Cloudiway deals with source and target throttling automatically;
  • no interruption to the day-to-day running of your business; and,
  • migration monitoring tools and logs available throughout migration.

Solution details

Mail migration
Folder migration:
During the migration, the platform recreates the exact folder tree as in the source mailbox.
Delta passes: You can perform several passes. This allows you, for example, to migrate all your data during a few days or a few weeks and perform a final delta pass over the last weekend.
For Office 365 to Office 365 the platform supports the synchronization between the source and the target mailbox. All deletions and modifications of folders and mails are propagated.
Migration between dates: You can also migrate mails created after a given date (for instance, the last 6 months) or mails between two dates. This allows you to migrate the x last months of mails from your users and then migrate older mails after you go live.
Archives: Cloudiway supports the migration to Office 365 archives: this allows you to migrate mails older than xx months to the Office 365 archives to prevent downloading the entire mailbox to the Outlook OST files.
Rooms and equipment migration: The platfrom includes a tool to recreate and migrate Office 365 rooms and equipment to the target tenant.
Coexistence during calendar migration, rooms reservation and calendar migration: During the calendar migration, the link between users and rooms calendars are preserved. Therefore, an organizer who has created an appointment and reserved a room can still cancel or update the appointment after  migration (see below for more information).
Batch migration: You can create a batch of users to arrange your migration into batches (VIPs, weekly, etc.)
File migration:

  • OneDrive is migrated to OneDrive
  • Permissions are preserved
  • The “Shared with me” view in OneDrive is updated: users can see the list of docs shared with them
  • The platform provides an online tool that creates an administrator account that has access to all your users’ OneDrive accounts.
  • No need to collect the passwords of your users
  • Delta passes supported
  • Batch migration: You can create a batch of users to arrange your migration into batches (VIPs, weekly, etc.)

Performance and scalability Cloudiway supports large cloud migrations and on-premises migrations. The on-demand migration engine is able to allocate the capacity of migration that you need to migrate the volume of data of your choice in the time slot that you have allocated for your migration. For instance, during a recent large migration, we migrated 15 Tb in three weeks, with an average migration of 600 GB/day. If our partner had needed to perform the migration in eight days instead of 20, we would have doubled the capacity of migration that we had allocated.


There are several limitations that you must be aware of when you’re performing a migration from Office 365 to Office 365.
Office 365 can heavily throttles users. When you perform too many calls, Office 365 begins throttling and decreases the number of calls that can be performed each minute, thus reducing the migration throughput. Cloudiway constantly attempts to work at the maximum capacity allowed by Office 365 and is able to achieve excellent throughput (500 GB to 1TB per day).

Cutover (‘one-shot’ or ‘big bang’) migration vs coexistence

A cutover migration is a strategy where all users are switched over at the same time. For example, all users are migrated over a weekend in a single migration pass. This strategy is the simplest and fastest to implement. If you have a lot of users, your migration might take more than a couple of days, so coexistence might be an option. Coexistence is where both systems will be live for some time. You will use a mechanism based on forwarders to ensure that migrated and non-migrated users will be able to communicate with each other throughout the migration process (learn more about coexistence).

Coexistence considerations

Imagine that you have 50% of your users already migrated to Office 365 and 50% still in the old tenant. A collaborator, Bob, sets up a physical meeting or an online meeting. Some problems arise:

  • Which collaborative solution will Bob use for sharing his screen? Lync for migrated users or old tenant + for non-migrated users?
  • What booking system will Bob use to book a room?
  • Where will Bob store the meeting minutes? In old One Drive or in a new one?

To avoid having to find solutions to these questions, it’s better to switch all users over at the same time.