Re: SMTP store and forward requires DSN for integrity (was Re:Clueless anti-virus )

[Douglas Otis <dotis () mail-abuse org>]

On Dec 9, 2005, at 4:09 PM, Robert Bonomi wrote:
> > >
> >
> > 1) Malware detection has a 0% false positive.
>
> If there is a 'false positive' detecting malware, it is a near  
> certainty that the "legitimate" message so classified does *NOT*  
> have a FORGED ADDRESS.

When there is some percentage of false-positive detection, there will  
be a number of messages that will fall into the "should not have been  
rejected" category, where indeed the return-path is not likely to  
have been forged, and a DSN would be of value to the sender.  When a  
DSN is sent, the sender will be able to take corrective action.   
There is also a percentage of messages where malware detection is  
valid, but nonetheless the return-path is also valid.  (Perhaps  
overwritten by the provider.)

You are judging this situation based upon only the wrong choice as  
having been made.  AV filtering is not the only situation where a DSN  
exploit is used, and there is no way to be sure about a choice of  
discarding the DSN.  Discarding DSNs _will_ degrade the integrity of  
email delivery.  As the recipient of the DSN is _always_ the best  
judge whether the DSN was sent to a forged return-path, why not take  
advantage of that superior knowledge?  Automate the process so the  
DSN recipient is able to immediate rejects _all_ invalid DSNs.   
Overall, email transactions will be faster, and DSN exploits will  
soon disappear.

-Doug