Re: NDNs considered harmful

 On 12/08/2010 15:32, John R Levine wrote:
> > True statement, but that means the senders of the other 5% are now left
> > in the dark as to what happened to their mail.
> > Is there a proposed solution to that?
> Talking out of my hat here, it is my impression that spam is much more 
> likely to be sent to bogus addresses than legit mail is, so however 
> the spam fraction of your mailstream, the spam fraction of your 
> bounces is likely to be even higher.
> On my tiny mail system, most but not quite all of the bounces can be 
> handled as rejections at SMTP time.  The ones I can't are generally 
> deliveries to scripts where the script decides whether it can accept 
> the mail.  When those say nope, can't deliver that, when is it worth 
> generating a bounce?
We have had several cases where our customers have been blacklisted by 
their ISP for sending 'spam', when, in fact, they have just been sending 
NDNs to all the spam they receive.
This is really quite tricky to handle in these cases - usually we just 
turn off the NDN sending.
(It's tricky in these cases because it's a 'non-standard' setup - with a 
catch-all POP3 account at an ISP, then a mail collector collecting from 
there, and sorting messages out and rejecting messages to unrecognised 
users - what should happen there? You can't do an SMTP reject, because 
the message has already been 'accepted for final delivery' by the ISP, 
so you have to send an NDN or not - the user isn't going to read the 
messages, so an NDN is appropriate, but causes problems.)