Security :: How To Get Email Address From AD

i have an aspx page which on page load needs to populate a text box with the current users email address (user is in Active Directory), any body know how to retrieve the email address from Active Directory, i have read this article on the web but am a bit confused

string userName = Environment.UserName;
string domainName = Environment.UserDomainName;
//Set the correct format for the AD query and filter
string ldapQueryFormat = @"LDAP://{0}.com/DC={0},DC=com";
string queryFilterFormat = @"(&(samAccountName={0})(objectCategory=person)(objectClass=user))";
SearchResult result = null;
using(DirectoryEntry root = newDirectoryEntry(rootQuery))
{
using(DirectorySearcher searcher = new DirectorySearcher(root))
{
searcher.Filter = searchFilter;
SearchResultCollection results = searcher.FindAll();
result = (results.Count != 0) ? results[0] : null;
}
}
string primaryEmail = result.Properties["mail"][0] as string;

There is no defintion of rootQuery- so not sure what that is, or a definition for searchFilter