dead letter recieved from cron

[Tapas Mishra]

On Wed, Sep 29, 2010 at 3:34 PM, Ahmed Kamal <ahmed.kamal at canonical.com> wrote:
>  These seem to be the "output" of a cron job. It seems like the server is
> configured to auto-update itself. Any output cron generates gets sent by
> email. dead.letter is when the mta (mail server) cannot deliver that email

Yes it is configured to auto update.Where is this mta trying to
deliver the mail.