[Serializable]
public class MsmqLog
{
    public string GUID { get; set; }
    public string EMLogJson { get; set; }
    public DateTime CreateTime { get; set; }
}

//1.为MessageQueue对象设置Formatter属性
private MessageQueue _msgQueue;
_msgQueue = new MessageQueue(_pathQueue);
_msgQueue.Formatter = new XmlMessageFormatter(new Type[] { typeof(MsmqLog) });

//2.为Message对象设置Formatter属性
MsmqLog msmqLog = new MsmqLog
{
    GUID = Guid.NewGuid().ToString(),
    EMLogJson = jsonLogStr,
    CreateTime = DateTime.Now
};
Message msg = new Message();
msg.Body = msmqLog;
msg.Formatter = new XmlMessageFormatter(new Type[] { typeof(MsmqLog) });