Default folder Root not found | Merge-MailboxFolder

[Skeddon]

Hi, when I use the following command:

.\Merge-MailboxFolder.ps1 -Copy -SourceMailbox $SourceMailbox -TargetMailbox $targetMailbox -MergeFolderList @{"Inbox"= "WellKnownFolderName.Inbox"; "Sent Items"= "WellKnownFolderName.SentItems"} -Office365 -OAuth -OAuthTenantId $tenantId -OAuthClientId $clientId -ProcessSubfolders -OAuthSecretKey $secretKey -LogFile "C:\Users\USER\Documents\Scripts\Logs.txt" -DebugLogFile

With some mailboxes I'm getting the following error while others work fine:

PS C:\scripts> C:\Users\USER\Documents\Scripts\Run_ALSO_Merge-MailboxFolder.ps1
4/15/2026 3:12:21 PM [Merge-MailboxFolder.ps1] Merge-MailboxFolder.ps1 version 1.4.3 starting
4/15/2026 3:12:21 PM [LoadEWSManagedAPI] Using EWS Managed API found at: C:\scripts\Microsoft.Exchange.WebServices.dll

Processing mailbox mail@domain1.de
4/15/2026 3:12:22 PM [ErrorReported] ERROR (ThrottledFolderBind): Exception calling "Bind" with "3" argument(s): "The s
pecified object was not found in the store., Default folder Root not found."
Failed to open target message store (mail@domain2.com)
4/15/2026 3:12:22 PM [Merge-MailboxFolder.ps1] Script finished in 00:00:00.2780000

The log file says the following:

4/15/2026 3:12:21 PM [Merge-MailboxFolder.ps1] Merge-MailboxFolder.ps1 version 1.4.3 starting
4/15/2026 3:12:21 PM [LoadLibraries] Searching for DLL: Microsoft.Exchange.WebServices.dll
4/15/2026 3:12:21 PM [LoadLibraries] Loading Microsoft.Exchange.WebServices.dll v15.00.0913.015 found at: C:\scripts\Microsoft.Exchange.WebServices.dll
4/15/2026 3:12:21 PM [LoadEWSManagedAPI] Using EWS Managed API found at: C:\scripts\Microsoft.Exchange.WebServices.dll
4/15/2026 3:12:21 PM [CreateService] Currently caching 1 ExchangeService objects
4/15/2026 3:12:21 PM [ThrottledFolderBind] Attempting to bind to folder MsgFolderRoot (mail@domain1.de)
4/15/2026 3:12:21 PM [ThrottledFolderBind] Successfully bound to folder MsgFolderRoot (mail@domain1.de)
4/15/2026 3:12:21 PM [CreateService] Currently caching 2 ExchangeService objects
4/15/2026 3:12:21 PM [ThrottledFolderBind] Attempting to bind to folder MsgFolderRoot (mail@domain2.com)
4/15/2026 3:12:22 PM [ErrorReported] ERROR (ThrottledFolderBind): Exception calling "Bind" with "3" argument(s): "The specified object was not found in the store., Default folder Root not found."
4/15/2026 3:12:22 PM [ThrottledFolderBind] FAILED to bind to folder MsgFolderRoot (mail@domain2.com)
4/15/2026 3:12:22 PM [Merge-MailboxFolder.ps1] Script finished in 00:00:00.2780000

Any idea how to solve this issue?

[David-Barrett-MS]

The scipt impersonates the source mailbox, so you'll need to ensure that the source mailbox has FullAccess permissions to the target mailbox to be able to copy between. That's the most likely scenario here - lack of permission to target.