Failed to import mail enabled folders because objects with duplicate PrimarySmtpAddress were found in the input file. That ...

Failed to import mail enabled folders because objects with duplicate PrimarySmtpAddress were found in the input file. That indicates a misconfiguration on your Exchange deployment. After fixing the problem, you can rerun the script Export-MailPublicFoldersForMigration.ps1 on your Exchange server, followed by the script Import-MailPublicFoldersForMigration.ps1 on Exchange Online to update mail enabled folders in Active Directory.