Hi YukiSun,
I was able to find more information in the EWS logs, thanks to an old forum post I found. The error is related to users using Search/Find People in Outlook. I spot checked one log each on all 4 servers, all 4999 related EWS log entries the same. Outlook is O365 semi-annual channel. Different users. Pretty sure desktop app. (Not all users have phones, ActiveSync is only turned on for those who do and most don't use the Outlook app on their phone. OWA is turned off for everyone, we don't use it.) I can only post partial log entry, but the rest repeats same issue.
2020-08-10T14:23:17.468Z,<GUID>,15,1,1979,3,Unknown,,Negotiate,true,<user>,<domain>,Microsoft Office/16.0 (Windows NT 10.0; Microsoft Outlook 16.0.12527; Pro),Target=None;Req=V2016_06_30/V2016_06_30;,<IP>,<ServerB2>,<ServerA1.FQDN>,FindPeople,500,1161,,ErrorInternalServerError,<user>,,,<GUID>,PrimaryServer,LocalTask,0,0,0,0,0,,,,,,,,,,,,,,,,,,,,...
...ServiceDiagnostics_SendWatsonReportOnUnhandledException=System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary. at System.ThrowHelper.ThrowKeyNotFoundException() at System.Collections.Generic.Dictionary2.get_Item(TKey key) at Microsoft.Exchange.Services.Core.DataConverter.ToServiceObjectPropertyListBase.AddFromSchemaPropertyList(Shape shapeToAddFrom ShapeEnum shapeEnum) at Microsoft.Exchange.Services.Core.DataConverter.ToServiceObjectPropertyListBase.SelectProperties(IMinimalCallContext callContext) at Microsoft.Exchange.Services.Core.DataConverter.ToServiceObjectPropertyListBase..ctor(IMinimalCallContext callContext Shape shape ResponseShape responseShape) at Microsoft.Exchange.Services.Core.Types.Persona.GetPropertyListForPersonaResponseShape(PersonaResponseShape personaResponseShape) at Microsoft.Exchange.Services.Core.SearchPeopleInDirectory.ExecuteInternal() at Microsoft.Exchange.Services.Core.SearchPeopleInDirectory.Execute() at Microsoft.Exchange.Services.Core.SearchPeopleInMailboxAndDirectory.Execute() at Microsoft.Exchange.Services.Core.FindPeople.Execute() at Microsoft.Exchange.Services.Core.ExceptionHandler
1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) at Microsoft.Exchange.Services.Core.BaseStepServiceCommand3.InternalExecuteStep(Boolean& isBatchStopResponse) at Microsoft.Exchange.Services.Core.ServiceCommandBase
1.<ExecuteStep>b__82_0() at Microsoft.Exchange.Services.Core.ServiceCommandBase1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() at Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func
2 filterDelegate Action1 catchDelegate);BaseServiceTask_SendWatsonReportOnGrayException=Microsoft.Exchange.Common.GrayException ---> System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary. at System.ThrowHelper.ThrowKeyNotFoundException() at System.Collections.Generic.Dictionary
2.get_Item(TKey key) at Microsoft.Exchange.Services.Core.DataConverter.ToServiceObjectPropertyListBase.AddFromSchemaPropertyList(Shape shapeToAddFrom ShapeEnum shapeEnum) at Microsoft.Exchange.Services.Core.DataConverter.ToServiceObjectPropertyListBase.SelectProperties(IMinimalCallContext callContext) at Microsoft.Exchange.Services.Core.DataConverter.ToServiceObjectPropertyListBase..ctor(IMinimalCallContext callContext Shape shape ResponseShape responseShape) at Microsoft.Exchange.Services.Core.Types.Persona.GetPropertyListForPersonaResponseShape(PersonaResponseShape personaResponseShape) at Microsoft.Exchange.Services.Core.SearchPeopleInDirectory.ExecuteInternal() at Microsoft.Exchange.Services.Core.SearchPeopleInDirectory.Execute() at Microsoft.Exchange.Services.Core.SearchPeopleInMailboxAndDirectory.Execute() at Microsoft.Exchange.Services.Core.FindPeople.Execute() at Microsoft.Exchange.Services.Core.ExceptionHandler1.Execute(IRequestDetailsLogger logger CreateServiceResult createServiceResult Int32 index ExecutionOption executionOption) at Microsoft.Exchange.Services.Core.BaseStepServiceCommand
3.InternalExecuteStep(Boolean& isBatchStopResponse) at Microsoft.Exchange.Services.Core.ServiceCommandBase1.<ExecuteStep>b__82_0() at Microsoft.Exchange.Services.Core.ServiceCommandBase
1.<>c__DisplayClass88_0.<ExecuteHelper>b__0() at Microsoft.Exchange.Common.IL.ILUtil.DoTryFilterCatch(Action tryDelegate Func2 filterDelegate Action
1 catchDelegate) at Microsoft.Exchange.Services.Core.ServiceDiagnostics.
Here is the old forum post I found, BUT his cause is NOT my cause. We don't have MACs, and none of the users in the logs I checked have delegate/Send as/Full permissions on any other mailbox but their own. The post just led me to the EWS logs.
Joan