Public Folder migration - TransientFailureSource error

Question

Migrating public folders from Exchange 2019 to Exchange online in a hybrid setup.

4 target PF mailboxes

3 of them seems to migrate data fine

1 of them can't even start migration

The error says TransientFailureSource

From the map.csv it seems that it is the NON_IPM_SUBTREE that gives troubles.

I have searched for days for a solution. Can someone help?

Answer 1

Hi @TN,

Thanks for posting in our Q&A forum!

Based on the error message and the map.csv file, it seems that you have some mail-enabled public folders under the NON_IPM_SUBTREE folder, which can cause issues during the migration process.

One possible solution is to download and run the ValidateMailPublicFolders script on your Exchange Server on-premises. The script reports orphaned mail-enabled public folders and mail-enabled public folders found under the NON_IPM_SUBTREE folder. https://learn.microsoft.com/en-us/exchange/troubleshoot/public-folders/public-folder-migration-fails

Another possible solution is to create a new target mailbox (empty) and change the source database to a new database. This may resolve the TransientFailureSource error. See: https://officeapps.medium.com/transient-failure-error-exchange-on-premise-to-o365-3d4fefb777a6

You can also check out some best practices for public folder preparation before migrations, such as finding out stale or unwanted public folders, validating existing public folders for known issues, checking the size of existing public folders and items, and creating the mapping file and target PF mailboxes.

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