If I wipe out my account and start over, it will sync up for a little while and then start failing. I see log messages such as this:
5:13:54 PM MailClient.Accounts.ConnectionException: Requested value 'GroupMailbox' was not found. ---\> System.ArgumentException: Requested value 'GroupMailbox' was not found.
5:13:54 PM at System.Enum.EnumResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument)
5:13:54 PM at System.Enum.TryParseEnum(Type enumType, String value, Boolean ignoreCase, EnumResult& parseResult)
5:13:54 PM at System.Enum.Parse(Type enumType, String value, Boolean ignoreCase)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.EwsUtilities.Parse[T](String value)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.EwsXmlReader.ReadElementValue[T]()
5:13:54 PM at Microsoft.Exchange.WebServices.Data.EmailAddress.TryReadElementFromXml(EwsServiceXmlReader reader)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ComplexProperty.InternalLoadFromXml(EwsServiceXmlReader reader, XmlNamespace xmlNamespace, String xmlElementName, Func`2 readAction)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ComplexProperty.LoadFromXml(EwsServiceXmlReader reader, XmlNamespace xmlNamespace, String xmlElementName)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ComplexProperty.LoadFromXml(EwsServiceXmlReader reader, String xmlElementName)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ComplexPropertyDefinitionBase.InternalLoadFromXml(EwsServiceXmlReader reader, PropertyBag propertyBag)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ContainedPropertyDefinition`1.InternalLoadFromXml(EwsServiceXmlReader reader, PropertyBag propertyBag)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ComplexPropertyDefinitionBase.LoadPropertyValueFromXml(EwsServiceXmlReader reader, PropertyBag propertyBag)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.PropertyBag.LoadFromXml(EwsServiceXmlReader reader, Boolean clear, PropertySet requestedPropertySet, Boolean onlySummaryPropertiesRequested)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.EwsServiceXmlReader.ReadServiceObjectsCollectionFromXml[TServiceObject](XmlNamespace collectionXmlNamespace, String collectionXmlElementName, GetObjectInstanceDelegate`1 getObjectInstanceDelegate, Boolean clearPropertyBag, PropertySet requestedPropertySet, Boolean summaryPropertiesOnly)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.GetItemResponse.ReadElementsFromXml(EwsServiceXmlReader reader)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ServiceResponse.LoadFromXml(EwsServiceXmlReader reader, String xmlElementName)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.ParseResponse(EwsServiceXmlReader reader)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.ReadResponse(EwsServiceXmlReader ewsXmlReader)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.SimpleServiceRequestBase.ReadResponseXml(Stream responseStream)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.SimpleServiceRequestBase.ReadResponse(IEwsHttpWebResponse response)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ExchangeService.InternalBindToItems(IEnumerable`1 itemIds, PropertySet propertySet, ServiceErrorHandling errorHandling)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToItem(ItemId itemId, PropertySet propertySet)
5:13:54 PM at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToItem[TItem](ItemId itemId, PropertySet propertySet)
5:13:54 PM at MailClient.Protocols.Exchange.ExchangeCalendarSynchronizer.ConvertApplicationData(ExchangeService service, EventItem item, Func`2 getChildren)
5:13:54 PM at MailClient.Protocols.Exchange.ExchangeItemSynchronizer`2.Upload(IItemUploadContext`1 uploadContext, Folder folder, IEnumerable`1 items, CancellationToken cancellationToken)
5:13:54 PM at MailClient.Protocols.Common.ItemSynchronizer`2.\<\>c\_\_DisplayClass29\_0.<enqueueupload>b__0(WorkerStatus status, CancellationToken cancellationToken)<br>5:13:54 PM at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)<br>5:13:54 PM --- End of inner exception stack trace ---<br>5:13:54 PM at MailClient.Protocols.Exchange.ExchangeGenericCommand.Execute(WorkerStatus status)<br>5:13:54 PM at MailClient.Commands.Command.Process(WorkerStatus status)</enqueueupload>
At this point the app can no longer receive email, calendar entries or anything else. I’ve tried multiple installations on multiple computers to test. The same account works just fine with both Windows 10 Mail/Calendar/People and Microsoft Outlook. Only emClient has the issue.