This article explains how Cloudiway migrates calendars.

Main features

  • Supports delta passes.
  • Calendars are synchronized. Updates and deletions between two passes are propagated.
  • Owner Field is migrated correctly (despite the fact that Exchange does not allow you to set/modify this field).
  • Links between appointments are preserved (after the migration, if a user cancels an appointment, everybody will receive the cancellation).
  • Rooms and equipment appointments are migrated.
  • Permissions and delegations on calendars are migrated.
  • All calendars are migrated (primary and additional calendars).


To ensure a proper migration of all types of entries, the timezone of mailboxes should be set properly before you run the migration.

How are calendars migrated?

When migrating to Office 365, Cloudiway  maintains the links between calendar entries.
This means that if a user modifies or cancels an appointment after it is migrated, the modification is propagated to all the attendees.

Technically, in Exchange, owner and attendee appointments are linked by a property named CleanGlobalObjectID.
Cloudiway reads CleanGlobalObjectID in the owner entry once migrated and sets it to the entry of the attendee.

During migration, the calendar of an attendee can be migrated before the calendar of an owner. Therefore calendar entries can be linked only after all calendars have been migrated

Once you have completed the migration of all the calendars, go to the mail migration global actions menu and run the Calendar Post Processing Task.

Google migration notes:

Additional calendars are migrated (primary and secondary).
However, Google calendars don’t have a creator field.
It’s not possible to know who has created the additional (secondary) calendars.
When the permissions are analysed, all we get is a list of owners, and a calendar can contain several owners.
The platform cannot determine who created the calendar and an arbitrary decision is made to migrate the calendar to the first owner found.
Since permissions are migrated, the user should have permissions to the calendar even if it’s migrated in another mailbox.

For Google to Office 365, calendar migration does not propagate changes to appointments or deletions.

Translation of addresses

Adresses found in permissions, owner (organizer), recipients and optional recipients are automatically converted during the migration.
The process uses the migration list as its mapping table.
It is important to define ALL the users and groups in the migration list before you start migrating your first mailbox.
If an entry is missing, any email addresses found in an appointment will not be converted. In particular, this will impact the migration of permissions and the migration of the organizer field (if the organizer field is not migrated correctly, since only the organizer is allowed to make a modification to a meeting, the meeting will become read only for everybody).