If you use sendmail on quimby, you might add an alias like this:

ding: "|/local/bin/nntp-post local.ding --delete=NNTP-Posting-Host"

Actually, to make the news-to-mail and mail-to-news gatewaying
complete, I'd setup the ding newsgroup as being moderated.  (Use an
`m' instead of a `y' as the 3rd argument to ctlinnd.)  Have
ding-moderator@gnus.org be the moderator (see the moderators file,
often /etc/news/moderators; see also moderators(5)).  Then, I'd
create aliases like this:

ding: ding-list ding-news

ding-list: :include:/whatever/lists/ding

ding-news: "|/local/bin/nntp-post local.ding
 --insert=Approved:auto
 --delete=NNTP-Posting-Host"

ding-moderator: ding

Or some such.

So, mail sent to `ding@gnus.org' goes to everyone on the mailing
list, and also gets fed to the nntp server after having an Approved
header added.

When someone posts an article to the newsgroup, it won't
(ordinarily) have the Approved header, and so inn will mail it to
ding-moderator.  Mail to ding-moderator gets forwarded to everyone
on the ding mailing list, and also gets fed back to the nntp server
after having the Approved header added.

M.