Get huge email list from Active Directory

DirectoryEntry entry = new DirectoryEntry("Domain", "UserName", "Password", AuthenticationTypes.None);
DirectorySearcher dSearch = new DirectorySearcher(entry);
dSearch.SearchScope = System.DirectoryServices.SearchScope.Subtree;
dSearch.ReferralChasing = ReferralChasingOption.All;
dSearch.PageSize = 5000;
dSearch.Filter = "(&(objectClass=user))";
foreach (SearchResult sResultSet in dSearch.FindAll())
{
if (sResultSet.Properties["mail"].Count > 0)
strClientEmails += sResultSet.Properties["mail"][0].ToString() + ",";
}