List < string > strList=new List < string > (); strList.Add("crossware365.com"); if (EmailProperties.ContainsKey("SMTPRCPTTO")) { foreach(string strItem in strList) { if (EmailProperties["SMTPRCPTTO"].IndexOf(strItem,StringComparison.OrdinalIgnoreCase) >= 0) { return false; } } } return true;