Re: Is predictable spam filtering a vulnerability?

[Chris Brown <chris@xxxxxxxxxxx>]

Aaron Cake wrote:

> Imagine if I decided to use a spam fitler against someone else...I make an
> email that contains known rejected words. I send that email, setting the
> "FROM" address and header to be that of my victim. If I send out hundreds of
> these messages, I can use someone else's spam filter to mail-bomb my victim
> with "rejected" messages.
>  
This definitely is a problem, but not just like you describe. Spammers 
themselves do the same thing based simply on the way SMTP works. At the 
ISP I work for we've had tons of problems with a spammer (or multiple 
spammers) using an address from one of our domains as the sender and 
then a bad recipient address and sending thousands of messages. The 
recipient server bounces messages back to the apparent sender, 
effectively mail-bombing them like you describe.  Its even worse when 
the victim address doesn't actually exist because then the postmaster 
address at both ends gets all kinds of warnings as well.

I've seen some ISPs have started to block mail sent by <> to put an end 
to this sort of thing, but that doesn't seem like a very good solution 
as it probably blocks legitimate bounce messages.

Chris