Don't use obsolete In-Reply-To format in messages (Bug#64454)

When creating a new message, message-send-mail uses an obsolete format
for the In-Reply-To header that includes additional information about
the originating message.  This patch changes the default to use the
rfc5322 approved format, but allow the obsolete format through a
defcustom.

* lisp/gnus/message.el (message-make-in-reply-to): Return only the
message-id of the originating message (the default) unless the new
custom variable message-header-use-obsolete-in-reply-to is non-nil.
* doc/misc/message.texi: Document the new custom variable
message-header-use-obsolete-in-reply-to.
* etc/NEWS: Update NEWS.

1 files changed, 6 insertions, 0 deletions

diff --git a/doc/misc/message.texi b/doc/misc/message.texi
index bd20aec5bc6..509bbd5b575 100644
--- a/doc/misc/message.texi
+++ b/doc/misc/message.texi
@@ -1791,6 +1791,12 @@ member list with elements @code{CC} and @code{To}, then
 @code{message-carefully-insert-headers} will not insert a @code{To}
 header when the message is already @code{CC}ed to the recipient.
 
+@item message-header-use-obsolete-in-reply-to
+@vindex message-header-use-obsolete-in-reply-to
+When non-@code{nil}, use an obsolete form of the @code{In-Reply-To}
+header that includes a parenthetical phrase with details of the
+originating email following the message id.  The default is @code{nil}.
+
 @item message-syntax-checks
 @vindex message-syntax-checks
 Controls what syntax checks should not be performed on outgoing posts.