I am having difficulty retrieving all mailboxes in our Exchange 5.5 server. This code works for Exchange 2000, but returns an empty result set for 5.5:

			

			Hashtable env = new Hashtable(10);
			

			env.put(Context.INITIAL_CONTEXT_FACTORY,
			

			"com.sun.jndi.ldap.LdapCtxFactory");
			

			env.put(Context.PROVIDER_URL, url);
			

			env.put(Context.SECURITY_AUTHENTICATION, "simple");
			

			env.put(Context.SECURITY_PRINCIPAL, username);
			

			env.put(Context.SECURITY_CREDENTIALS, password);
			

			

			context = new InitialDirContext(env);
			

			

			String [] RETURN_ATTRIBUTES = {"..."};
			

			

			Attributes matchAttrs = new BasicAttributes(true);
			

			

			// Here is the offending attribute
			

			matchAttrs.put(new BasicAttribute("mail", null));
			

			

			return context.search(key, matchAttrs, RETURN_ATTRIBUTES);
			

		

I can retrieve all 'real' users by searching against the surname, and the mail attribute does in fact exist. Is the "null" attribute value the issue? Is there a better way to search for all entries that have a valid value for the said attribute. Any assistance would be appreciated.