I have a simple login form to authenticate users.  A code segment looks like
this:

           search.PropertiesToLoad.Add("cn");

           search.PropertiesToLoad.Add("name");

           search.PropertiesToLoad.Add("givenname");

           search.PropertiesToLoad.Add("sn");

           search.PropertiesToLoad.Add("mail");

           SearchResult result = search.FindOne();

           string fullname = (string)result.Properties["name"][0];

           string uname = (string)result.Properties["cn"][0];

           string firstname = (string)result.Properties["givenname"][0];

           string lastname = (string)result.Properties["sn"][0];

           string mmail = (string)result.Properties["mail"][0];

When I tested with several user accounts, some authenticated perfectly fine,
some threw the exception "Index was out of range. Must be non-negative and
less than the size of the collection. Parameter name: index"   .  The
exception was eventually traced to the " string mmail =
(string)result.Properties["mail"][0]; " statement.  So is this because that
user has no email in AD?  How best to handle this?

Am a newbie in this area.  Any insight appreciate.