How to fix calendar migration errors caused by duplicate calendar folders (4373230)

How to fix calendar migration errors caused by duplicate calendar folders

A few mailboxes experienced the following problems during a calendar migration:

• Some calendars did not migrate at all, even after re-running the migration and refreshing the user account.
• The following error occurred for some mailboxes: Failed to find calendar folder XY during appointment estimation.

This means that the mailbox has two calendars with the same name, which causes a conflict during the migration.

The root cause of this issue is that some users have two calendars with the same name.

To resolve this issue, please try below methods :

1) Use EWS Editor to check the user account structure and look for duplicate calendar folders.
2) Use EWS Editor to remove or rename the calendar folder that is not required before retrying migration.
3) Use MFCMAPI to rename the unused calendar folder.
4) Use MFCMAPI to copy all calendar items from main calendar folder to the other duplicated calendar folder before retrying migration.