/// <summary>
        /// Sends 'New user' notification message to a platform owner
        /// </summary>
        /// <param name="user">User instance</param>
        /// <returns>Queued email identifier</returns>
        public virtual IList <int> SendUserRegisteredNotificationMessage(User user)
        {
            if (user == null)
            {
                throw new ArgumentNullException(nameof(user));
            }

            var messageTemplates = GetActiveMessageTemplates(MessageTemplateSystemNames.UserRegisteredNotification);

            if (!messageTemplates.Any())
            {
                return(new List <int>());
            }

            //tokens
            var commonTokens = new List <Token>();

            _messageTokenProvider.AddUserTokens(commonTokens, user);

            return(messageTemplates.Select(messageTemplate =>
            {
                var tokens = new List <Token>(commonTokens);
                _messageTokenProvider.AddPlatformTokens(tokens);

                var toEmail = _config.PlatformSettings.Email;
                var toName = _config.PlatformSettings.Name;

                return SendNotification(messageTemplate, tokens, toEmail, toName);
            }).ToList());
        }