Variable: display-time-mail-function
display-time-mail-function is a customizable variable defined in
time.el.gz.
Value
nil
Documentation
Function to call, for indicating existence of new mail.
If nil, that means use the default method: check that the file
specified by display-time-mail-file is nonempty or that the
directory display-time-mail-directory contains nonempty files.
Source Code
;; Defined in /usr/src/emacs/lisp/time.el.gz
(defcustom display-time-mail-function nil
"Function to call, for indicating existence of new mail.
If nil, that means use the default method: check that the file
specified by `display-time-mail-file' is nonempty or that the
directory `display-time-mail-directory' contains nonempty files."
:type '(choice (const :tag "Default" nil)
(function)))