Clement, I did the online translation. That was a nicely written article and very helpful. Thank you again for your help.
Date: Mon, 5 Nov 2012 21:41:30 +0100
Subject: Re: Lastlogon attribute
2012/11/5 jeevan kc <email@example.com>
The overlay will write the timestamp in authtimestamp operational attribute in the user entry.
I wrote an article on this but it's in French: http://coudot.blogs.linagora.com/index.php/post/2012/06/12/M%C3%A9moriser-la-derni%C3%A8re-authentification-dans-OpenLDAP
Maybe an online translation can help you.