Hi,
First write below code in web.config  </system.web> and before
</configuration>:
<system.net >
   <mailSettings >
   <smtp from="who@myhost.com">
     <network host="mail.myhost.net" userName="xxxxx" password="xxxx"/>
   </smtp>
 </mailSettings>
   </system.net >

Then try this code:
Configuration configurationFile =
WebConfigurationManager.OpenWebConfiguration("~\\Web.config");
       MailSettingsSectionGroup mailSettings =
configurationFile.GetSectionGroup("system.net/mailSettings") as
MailSettingsSectionGroup;
       if (mailSettings != null)
       {    
           int port = mailSettings.Smtp.Network.Port;    
           string host = mailSettings.Smtp.Network.Host;  
           string password = mailSettings.Smtp.Network.Password;    
           string username = mailSettings.Smtp.Network.UserName;

           lblHost.Text = host;
           lblUserName.Text = username;
           lblPassword.Text = password;
       }
Also include following namespaces:
using System.Configuration;
using System.Web.Configuration;
using System.Net.Configuration;