public static void Run() { // Set Exchange Server web service URL, Username, password, domain information string mailboxURI = "https://ex2010/ews/exchange.asmx"; string username = "******"; string password = "******"; string domain = "ex2010.local"; //ExStart: WorkingWithExtendedAttributesOfMessages // Connect to the Exchange Server NetworkCredential credential = new NetworkCredential(username, password, domain); IEWSClient client = EWSClient.GetEWSClient(mailboxURI, credential); { try { //Create a new Property PidNamePropertyDescriptor pd = new PidNamePropertyDescriptor( "MyTestProp", PropertyDataType.String, KnownPropertySets.PublicStrings); string value = "MyTestPropValue"; //Create a message MapiMessage message = new MapiMessage( "*****@*****.**", "*****@*****.**", "EMAILNET-38844 - " + Guid.NewGuid().ToString(), "EMAILNET-38844 EWS: Support for create, retrieve and update Extended Attributes for Emails"); //Set property on the message message.SetProperty(pd, value); //append the message to server string uri = client.AppendMessage(message); //Fetch the message from server MapiMessage mapiMessage = client.FetchItem(uri, new PropertyDescriptor[] { pd }); //Retreive the value from Message string fetchedValue = mapiMessage.NamedProperties[pd].GetString(); } finally { } } //ExEnd: WorkingWithExtendedAttributesOfMessages }