User Properties vs MAPI ExtendedPropertyDefinition RRS feed

  • Question

  • What is the difference between Extended Properties Definition created with EWS Managed API and User properties created with the outlook addin. 

    I can write a custom property like this using the  EWS Managed API:

         private void setProperty(Item item, Property prop) { 


              item.SetExtendedProperty(, Prop.value); 

              ConflictResolutionMode mode = ConflictResolutionMode.AlwaysOverwrite; 



    Where Prop is an object, that contains an Extended Property definition and object value:

    ExtendedPropertyDefinition prop = new ExtendedPropertyDefinition(

    DefaultExtendedPropertySet.PublicStrings, "Prop", MapiPropertyType.String);

    Inside of the Outlook Add-In User Properties are set using this method:

    mailItem.UserProperties.Add("PropName", Microsoft.Office.Interop.Outlook.OlUserPropertyType.olText).Value = PropValue;

    In EWS Managed API how do you access these properties set in the outlook addin? 

    Second Question:

    These properties set using the UserProperties, Add method, persist on message send. Do properties set to a mailItem using SetExtendedProperty, of EWS persist across message send. If not what property can be used to do so? 

    Milton Cody

    Tuesday, August 25, 2015 3:23 PM

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