嗯，您可以像这样声明变量

Hmm you can declare your variables like this

<appSettings>
    <add key="SmtpServerHost" value="********" />
    <add key="SmtpServerPort" value="25" />
    <add key="SmtpServerUserName" value="******" />
    <add key="SmtpServerPassword" value="*****" />
</appSettings>

并读为

string smtpHost = ConfigurationManager.AppSettings["SmtpServerHost"];
int smtpPort = Convert.ToInt32(ConfigurationManager.AppSettings["SmtpServerHost"]);