[SLL] mailhub relay without knowing accounts and throttling inbound by domain name and outbound with postfix?

[Glenn Stone]

On Thu, Feb 21, 2008 at 11:01:24AM -0600, Jeremy C. Reed wrote:
>By the way, it appears that some of the target mail servers aren't the 
>final destinations either as they accept mail from unknown users, for 
>example, I receive "status=sent (250 Ok: queued as 3CB08679499)" for 
>obviously bogus recipients.

Is somebody for whom you are providing the mailhub bouncing spam back to the
From: address?  This is a Bad Idea and generally Not Recommended; basically,
once spam has got beyond the initial SMTP transaction session and cannot be
simply 550'ed back into the real spammer's face, it's best to simply drop it
on the floor.  If somebody that's more or less under your control
(i.e. you're providing the mailhub *for them* and they're doing the sending)
is doing this, you may wish to have a word with them.  

I used to think that generating "user unknown" bounces back to From: or
From_ was a good idea; Dan Wilder taught me differently, and I later ended
up being on the receiving end of such things and know why... fortunately for
me, the joe jobber was generating patently bogus left-hand-sides, and the
domain for whom I was hosting explicitly did NOT want wild-card destinations
turned on... so it all worked out for the best; not one single bogus bounce
got through, and Postfix politely throttled things back well before they got
out of hand and could threaten my uptime.  

Just my suspicion as to what's going on.... sometimes the best solution is
less technical and more social engineering.  

-- Glenn