using System;

public class Program

{

    public static void Main()

    {

        var message = new Message();

        Console.WriteLine($"subject: {message.Subject}");

        var messageTag = message.Subject.Equals("Click Tracking Ping Message") ? MetricsConstants.ClickTrackingTag : MetricsConstants.MessageTag;

    }

}

​

public class Message {

    public string Subject { get; }

}

​

 public static class MetricsConstants

 {

     public const string MessageTag = "message:plain";

     public const string ClickTrackingTag = "message:click-tracking";

     public const string MessagesSent = "MessagesSent";

     public const string MessagesReceived = "MessagesReceived";

     public const string MessagesDeleted = "MessagesDeleted";

     public const string NdrsReceivedBySender = "NdrsReceivedBySender";

     public const string QueuedTime = "QueuedTime";

     public const string DeliveryTime = "DeliveryTime";

     public const string TotalTime = "TotalTime";

     public const string ProxyLatencyHeader = "X-ExclaimerProxyLatency";

     public const string PingMachineModHeader = "X-ExclaimerPingMachineMod";

     public const string ExchangeTag = "Exchange";

 }