Forum Discussion
Exchange 2019 Mailbox Migration Error - Folder conflicts with Exchange Online folder
Hi Exchange Experts,
I'm migrating a small Exchange 2019 environment to 365. Been pulling my hair out becuase of just one mailbox giving this error
Error description ---------------------------
Error: AggregateMailboxFolderConflictPermanentException: The folder 'Files' conflicts with Exchange Online folder 'Files', please move the messages to another folder and restart the job.
Data migrated: 0 B (0 bytes)
Migration rate:
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Migration user report:
5/14/2025 12:32:05 PM [MEUP300MB0105] Request processing continued, stage CreatingFolderHierarchy.
5/14/2025 12:32:05 PM [MEUP300MB0105] Stage: CreatingFolderHierarchy. Percent complete: 10.
5/14/2025 12:32:12 PM [MEUP300MB0105] Stage: CreatingFolderHierarchy. Percent complete: 10.
5/14/2025 12:32:12 PM [MEUP300MB0105] Fatal error AggregateMailboxFolderConflictPermanentException has occurred.
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It seems to be a system folder and I've tried to remove files from it (although there're no files in it) using MFCMAPI tool with no success. Renamed the folder and tried to re-run the migration with no luck.
Has anyone experience this issue? any thoughts or tips are much appreciated !
Thank you.
6 Replies
Hi there,
I’ve faced similar issues while migrating from Exchange 2019 to Office 365. Errors like AggregateMailboxFolderConflictPermanentException often happen because of system folder conflicts, and even empty or hidden folders can trigger them.
In my experience, using EdbMails Exchange Migration helped streamline the migration process:
Preserves mailbox hierarchy – All folders from the source Exchange mailbox, including subfolders and system folders, were migrated to Office 365 while keeping the same structure.
Concurrent mailbox migration – Allowed multiple mailboxes to migrate simultaneously, saving time.
Incremental migration – Any partially migrated data was synced without duplicating items on retry.
Direct Exchange 2019 → Office 365 migration – Enabled moving mailboxes, archive mailboxes, and public folders directly without needing PST exports.
With EdbMails, we were able to successfully migrate mailboxes while maintaining the same folder hierarchy in the target Office 365 mailboxes.
If you’re planning an Exchange 2019 → Office 365 migration, I’d recommend considering EdbMails Exchange Migration, especially when preserving mailbox structure is important.
Have you had a resolution to this error? I am seeing the same thing but the Files folder looks to be in all mailboxes, not sure why one or two are failing me with the same error you see.
I manage to resolve this by renaming "Files" to "MyFiles" and unhid the folder thru MFCMAPI tool (PR_ATTR_HIDDEN = False)
Hi Curious_Kevin16,
I managed to resolve this by renaming the "Files" folder to "MyFiles" and unhide the folder using MFCMAPI (PR_ATTR_HIDDEN = False).
My guess is that the user has created a folder called "Files" in their mailbox and this is conflicting with the system folder in EXO. Maybe have a chat to the user and see if they can rename it.
"Files" seems to be a system folder and you can't do much except renaming which we tried through MFCMapi with no luck, it still refers to the "Files' folder.
EXO shouldn't matter should it? as we're simply trying to remote move the mailbox and obviously there's no mailbox exists in EXO for this user yet.
