Re: [Exim] spam calls home

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 ?