I searched a lot for built web service like Google Talk, using Google Application Engine and Python.
For that first step is to check the status of online user on the Gmail. I found many code of it on python using XMPP library but it work only on python not using Google Application Engine.
There is also suggestion of using XMPP python API but for sending message we have to provide JID like app-id@appspot.com and message send.We can not send message from one email Id to another Email Id directly.
Now I want to perform Oauth authentication in python for gtalk at domain level can anyone tell me how to do this?
You can only send messages from your app.  There are two options:  your_app_id@appspot.com or anything@your_app_id.appspotchat.com.
If you wanted to behave like an arbitrary xmpp client, you'll have to use a third party xmpp library running over HTTP and handle the authentication with the user's XMPP server.
Gtalk Service On Google App Engine Using Python