This is ground that has been covered before in part by this list but
I'm afraid I havn't been able to find exactly what I want in the list
I would like to provide a means by which a person reading a message in a
converted list can respond to it - a reply button. The mailto URL goes
part of the way - you can specify the Subject: field along with the
In-Reply-To: and address fields for example. Al Gilman  provides a
link to an example using the mailto URL.
However, it doesn't provide all the functionality I'd like. There are
several services out on the Web now that allow users to read and compose
mail entirely using a browser (Eudora WebMail comes to mind). What I'd
like is the mail composition features of one of these services including
the ability to feed it the original email message that the response it to.
Earl Hood  suggested implementing just this in a previous post
(as mailform.cgi) but I'm not sure this actually exists yet.
Getting the email message itself to pass to this tools shouldn't be
too difficult - either retrieving it from a mbox or perhaps even from
the HTML itself. I notice that Achim who looks after the list archive
provides a CGI to do just this (/cgi-bin/extract-mbox).
(Come to think of it Achim, returning with type message/rfc822 rather
than text/plain may be an alternative solution depending on what helper
application a browser would use to read this).
The result would be the ability to respond to messages in the archive
with all the basic features you'd like in a mail composition tool
available including the text of the message for quoting.
Can anybody help?