private List <int> GetMailIndex(IMailClient client, string searchCriteria, string mailbox) { IEnumerable <int> strMsgIds = null; string mailIndexs = string.Empty; if (string.IsNullOrWhiteSpace(searchCriteria)) { mailIndexs = client.GetAllMessagesFlag(out strMsgIds, mailbox); } else { mailIndexs = client.SearchMail(searchCriteria, out strMsgIds, mailbox); } return(strMsgIds.ToList()); }