By default when this ODM feature is enabled, calendar items which have already been migrated to target mailbox may be wrongly deleted in these below special scenarios :
Scenario 1 :
For migration from multiple source mailboxes, when merging content from 2 or more separate source mailboxes into 1 target mailbox, after having already performed a first run for the first source mailbox, you are going to run another migration for the second source mailbox, & then following by subsequent source mailboxes, hence we may not want calendar items in target mailbox which have already been migrated from the earlier source mailboxes to get purged during later migrations if they do not exist in subsequent source mailboxes.
Scenario 2 :
After having already performed a primary to primary mailbox migration, you are going to proceed to migrate its archive mailbox at source to its primary mailbox at target for the same mailbox, hence we may not want calendar items which have already been migrated to primary mailbox at target to get purged.
This ODM engine configuration value is set to True by default, which means the calendar synchronization logic treats the source mailbox as the master copy.
As a result, calendar items in the target mailbox that were previously migrated from earlier source mailboxes may be deleted during subsequent migrations if they no longer exist in the new source mailboxes.
If this value is set to False, the ODM engine will not delete any calendar items that do not exist in the source mailbox.
ODM can be configured to not have the calendar sync deletes.
Note: This is an Organization wide change and cannot be implemented on a per mailbox level.
Please submit a Technical Support Case to request for this change.
