private static String getExpression(String message) {
		if(message.matches("(?i)^SEND MAIL [_a-z0-9-]+(\\.[_a-z0-9-]+)*@[a-z0-9-]+(\\.[a-z0-9-]+)*(\\.[a-z]{2,4})")){
			return "SEND MAIL";
		}
		else if(message.matches("(?i)^MAIL FROM [_a-z0-9-]+(\\.[_a-z0-9-]+)*@[a-z0-9-]+(\\.[a-z0-9-]+)*(\\.[a-z]{2,4})")){
			return "MAIL FROM";
		}
		if(message.matches("(?i)^SEND MAIL\\s*")){
			return "SEND ERROR 202";
		}
		else if(message.matches("(?i)^MAIL SUBJECT \".*\"")){
			return "MAIL SUBJECT";
		}
		else if(message.matches("(?i)^MAIL BODY \".*\"")){
			return "MAIL BODY";
		}
		else if(message.matches("(?i)^END SEND MAIL")){
			return "END SEND MAIL";
		}
		else if(message.matches("(?i)^CHECK CONTACT [_a-z0-9-]+(\\.[_a-z0-9-]+)*@[a-z0-9-]+(\\.[a-z0-9-]+)*(\\.[a-z]{2,4})")){
			return "CHECK CONTACT";
		}
		return "INVALID COMMAND ERROR";
	}