An error of the following form may be logged when attempting to switch or unswitch a mailbox to Office 365 after MS Dirsync:
2015-03-20 07:37:00.2110 PxE9C TxB A- C- M- Error System.Exception: The operation on mailbox "<mailbox>" failed because it's out of the current user's write scope. The action 'Set-Mailbox', 'EmailAddresses', can't be performed on the object '<mailbox>' because the object is being synchronized from your on-premises organization. This action should be performed on the object in your on-premises organization.
at DirectoryMigration.IDMObjectPair.Switch()
at Dell.MigrationManagerForExchange.Shared.Switching.O365SwitcherAndMatcher.Switch(Guid sourceGuid)
at Quest.MigrationManager.Exchange.O365ProvisioningWebService.O365ProvisioningProxy.<>c__DisplayClass7.<Switch>b__6()
at Quest.MigrationManager.Exchange.O365ProvisioningWebService.O365ProvisioningProxy.InvokeTryCatchAction(Action act) at Quest.MigrationManager.Exchange.O365UserProvisioning.O365UserProvisioning.CheckAndThrow(Func`1 exceptionFunc)
at Quest.MigrationManager.Exchange.O365UserProvisioning.O365UserProvisioning.Switch(Int32 mailboxId, Int32 collectionId, Boolean rollbackSwitchOnFail)