Variable: mail-interactive
mail-interactive is a customizable variable defined in sendmail.el.gz.
Value
t
Documentation
Non-nil means when sending a message wait for and display errors.
Otherwise, let mailer send back a message to report errors.
This variable was added, or its default value changed, in Emacs 23.1.
Probably introduced at or before Emacs version 23.2.
Source Code
;; Defined in /usr/src/emacs/lisp/mail/sendmail.el.gz
;;;###autoload
(defcustom mail-interactive t
;; We used to use a default of nil rather than t, but nowadays it is very
;; common for sendmail to be misconfigured, so one cannot rely on the
;; bounce message to be delivered anywhere, least of all to the
;; user's mailbox.
"Non-nil means when sending a message wait for and display errors.
Otherwise, let mailer send back a message to report errors."
:type 'boolean
:version "23.1") ; changed from nil to t