* lisp/calendar/diary-lib.el (diary-from-outlook-function): New variable.

(diary-from-outlook): Respect diary-from-outlook-function.

* doc/emacs/calendar.texi (Importing Diary):
Mention diary-from-outlook-function.

* etc/NEWS: Mention this.

doc/emacs/ChangeLog

@@ -1,3 +1,7 @@
+2013-05-04  Glenn Morris  <rgm@gnu.org>
+
+	* calendar.texi (Importing Diary): Mention diary-from-outlook-function.
+
 2013-03-17  Paul Eggert  <eggert@cs.ucla.edu>
 
 	doc: convert some TeX accents to UTF-8

doc/emacs/calendar.texi

@@ -1542,7 +1542,8 @@ variety of other formats.
 messages.  While viewing such a message in Rmail or Gnus, do @kbd{M-x
 diary-from-outlook} to import the entry.  You can make this command
 recognize additional appointment message formats by customizing the
-variable @code{diary-outlook-formats}.
+variable @code{diary-outlook-formats}.  Other mail clients can set
+@code{diary-from-outlook-function} to an appropriate value.
 
 @c FIXME the name of the RFC is hardly very relevant.
 @cindex iCalendar support

etc/NEWS

@@ -146,6 +146,12 @@ The default separator is changed to allow surrounding spaces around the comma.
 
 *** Battery information via the BSD `apm' utility is now supported.
 
+** Calendar and Diary
+
++++
+*** New variable `diary-from-outlook-function' for used by the command
+`diary-from-outlook'.
+
 ** cl-lib
 
 *** New macro cl-tagbody.

lisp/ChangeLog

@@ -1,3 +1,8 @@
+2013-05-04  Glenn Morris  <rgm@gnu.org>
+
+	* calendar/diary-lib.el (diary-from-outlook-function): New variable.
+	(diary-from-outlook): Respect diary-from-outlook-function.
+
 2013-05-04  Stefan Monnier  <monnier@iro.umontreal.ca>
 
 	* simple.el (read-expression-map): Use completion-at-point (bug#14255).

lisp/calendar/diary-lib.el

@@ -2611,14 +2611,23 @@ user is asked to confirm its addition."
           (diary-from-outlook-internal subject body)
           (message "Diary entry added"))))))
 
+(defvar diary-from-outlook-function nil
+  "If non-nil, a function of one argument for `diary-from-outlook' to call.
+If the current buffer contains an Outlook-style appointment message,
+this function should extract it into a diary entry.  If the argument is
+nil, it should ask for confirmation before adding this entry to the diary.
+For examples, see `diary-from-outlook-rmail' and `diary-from-outlook-gnus'.")
+
 (defun diary-from-outlook (&optional noconfirm)
   "Maybe snarf diary entry from current Outlook-generated message.
-Currently knows about Gnus and Rmail modes.  Unless the optional
-argument NOCONFIRM is non-nil (which is the case when this
-function is called interactively), then if an entry is found the
-user is asked to confirm its addition."
+Uses `diary-from-outlook-function' if that is non-nil, else
+`diary-from-outlook-rmail' for Rmail or `diary-from-outlook-gnus' for Gnus.
+Unless the optional argument NOCONFIRM is non-nil (which is the
+case when this function is called interactively), then if an
+entry is found the user is asked to confirm its addition."
   (interactive "p")
   (let ((func (cond
+               (diary-from-outlook-function)
                ((eq major-mode 'rmail-mode)
                 #'diary-from-outlook-rmail)
                ((memq major-mode '(gnus-summary-mode gnus-article-mode))