public static void DeleteAllUnreadMessages()
        {
            Credential = Preparation.GetUserCredential();

            var messages = Messages.ListMessages(Preparation.GetService(Credential), User, "in:inbox is:unread");

            if (!messages.Any())
            {
                return;
            }

            foreach (var message in messages)
            {
                Messages.DeleteMessage(Service, User, message.Id);
            }
        }
 static Gmail()
 {
     Credential = Preparation.GetUserCredential();
     Service    = Preparation.GetService(Credential);
 }