Ensure.Argument.NotNull(template);

            var users = _userRepo
                .AllIncluding(u => u.SentEmails);

            switch (template.QueueAfter)
            {
                case QueueAfter.RegistrationDate:
                    users = users.Where(ud => ud.RegisteredOn <= DateTime.Today.AddDays(template.QueueDays));
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }

            var asc = UserBase.GetAccountStateCode(template.QueueAccountState);
            return users
                .Where(u => u.AccountStateCode == asc
                         && u is Customer
                         && !u.SentEmails.Select(s => s.EmailTemplateId).Contains(template.Id))
                    .Select(user => user as Customer)
                    .ToList();