Re: [Exim] spam calls home

On Fri, Nov 28, 2003 at 09:08:38AM +0100, Leonardo Boselli said:
> On Thu, 27 Nov 2003, Walt Reed wrote:
> > > > Many spams now call home by requesting a 'zero byte' gif when you
> > > > open the page. This is also used for other people wanting to see if
> > > > you opened the mail. Are there any rules for checking this?
> > > this is an MUA issue, not an MTA issue, making it offtopic here.
> > Yeah, it's a little off topic, but it can by handled by preprocessing
> > before mail gets to a MUA as well.
> > Check out John Hardin's procmail security (google for it) which has some
> > filtering for this kind of thing.
>
> Consider one service we have here: The reservation for one laboratory are
> "blackboard handled" , that is one write his/her reservation on a
> blackboard. There is a camera that is pointed on that blackbord and write
> a file (actually a gif file ...) so one can look for reservations.
> If someone clean accuraely the board from any writing the compression
> program actually does not emit a blak file, but just a zero byte file (the
> file capture are archived as a transaction tool for resaervations !)
> So if you found a zero byte gif is not spam, but jjust a valuable
> indication (very valuable, since it means that you can use all
> laboratories !)
> If I send to someone that address haw would you cope with it ?

John's application would disable it (not delete it) AFAIK. Rather than
send an empty picture (which seems silly) why wouldn't you just emit a
text string that says that it's empty??