Migration Agent for Exchange (MAgE) logs the following error when connecting to source or target mailbox:
2018-11-30 15:01:02.9614 Px510 Tx19 A10 C38 M706 Trace TRG(Ews) Connect begin
2018-11-30 15:01:02.9614 Px510 Tx19 A10 C38 M706 Info Get user settings for email address: '<smtp@contoso.com>', autodiscover url: 'https://<target_autodiscover>/Autodiscover/Autodiscover.svc'
2018-11-30 15:01:03.0083 Px510 Tx19 A10 C38 M706 Trace Get user settings results : (UserDeploymentId) : 4b88b8cc-70fb-4b0d-839f-529bbddf7ea1; (InternalEwsUrl) : https://<target_EWS>/EWS/Exchange.asmx; (ExternalEwsUrl) : https://<souce_EWS>/ews/exchange.asmx;
2018-11-30 15:01:03.0083 Px510 Tx19 A10 C38 M706 Info Ews Connection. Url: 'https://<source_EWS>/ews/exchange.asmx' Username: 'target_service_account' Domain: '<target_domain>' Mailbox: '<smtp@contoso.com>' PreferredCulture: 'en-GB'
2018-11-30 15:01:03.3362 Px510 Tx19 A10 C38 M706 Trace TRG(Ews) Connect end
2018-11-30 15:01:03.3362 Px510 Tx19 A10 C38 M706 Error Microsoft.Exchange.WebServices.Data.ServiceResponseException: Unable to access an account or mailbox.
at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ProcessWebException(WebException webException)
at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ValidateAndEmitRequest(IEwsHttpWebRequest& request)
at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
at Microsoft.Exchange.WebServices.Data.ExchangeService.InternalBindToFolders(IEnumerable`1 folderIds, PropertySet propertySet, ServiceErrorHandling errorHandling)
at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToFolder(FolderId folderId, PropertySet propertySet)
at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToFolder[TFolder](FolderId folderId, PropertySet propertySet)
at MigrationManager.Exchange.MigrationConnectors.Ews.ProductionExchangeService.FolderBind(WellKnownFolderName name, PropertySet propertySet)
at MigrationManager.Exchange.MigrationConnectors.Ews.EwsSyncConnector.ConnectInternal()
at MigrationManager.Exchange.MigrationConnectors.Ews.EwsSyncConnector.Connect()
at MigrationManager.Exchange.Agent.Jobs.DisPlusO365JobBase.ConnectOverEws()
at MigrationManager.Exchange.Agent.Jobs.DisBaseJob.ConnectionOverEws()
at MigrationManager.Exchange.Agent.Jobs.DisBaseJob.PerformSync()
at MigrationManager.Exchange.Agent.Jobs.DisPlusO365JobBase.RunJob()