See the following: (the lines after the first one are the names of each SMTP setting in the HostSettings table)

//DotNetNuke.Entities.Host.HostSettings.GetHostSetting("");
//SMTPAuthentication
//SMTPEnableSSL
//SMTPPassword
//SMTPServer
//SMTPUsername

I've been using HostSettings hashtable to access those settings (as in PortalSettings.HostSettings(["SMTP..."]).toString())

Does it make any difference?