mail-use-dsn

mail-use-dsn is a variable defined in `sendmail.el'.
Its value is

nil

Documentation:
Ask MTA for notification of failed, delayed or successful delivery.
Note that only some MTAs (currently only recent versions of Sendmail)
support Delivery Status Notification.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.