Variable: mh-message-id-regexp
mh-message-id-regexp is a variable defined in mh-thread.el.gz.
Value
"^<.*@.*>$"
Documentation
Regexp to recognize whether a string is a message identifier.
Source Code
;; Defined in /usr/src/emacs/lisp/mh-e/mh-thread.el.gz
(defvar mh-message-id-regexp "^<.*@.*>$"
"Regexp to recognize whether a string is a message identifier.")