;; A NOV structure looks like this (must be prin1-able, so no defstruct):
["subject\tfrom\tdate"
- "references\tchars\lines"
+ "references\tchars\tlines"
"To: you\tIn-Reply-To: <your.mess@ge>"
(12345 67890) ;; modtime of the corresponding article file
(to in-reply-to)] ;; contemporary value of nnmail-extra-headers