Re: FW: ... the technique of Nolisting

[Larry Bolhuis <lbolhuis@xxxxxxxxxx>]

I'm not buying it. Spammers don't give a &(^% about RFC compliance. 
Often they start at the bottom of your MX records anyway because in many 
cases those don't have full spam protection and their nefarious crud is 
more likely to get past you. In addition they often try other addresses 
such as 'mail.yourdomain.com' because often those addresses are set up 
to allow inbound mail by authenticated users. Turns out though that 
often these will also accept mail destined for your domain without 
authentication and again the spammers win.

This also puts additional load on mail servers around the net as they 
attempt to get to the non-responsive server in the first MX. although in 
this regard it's much the same load as Greylisting adds.

- Larry

Graap, Kenneth wrote:
> I thought this was worth sharing with everyone...
>
> Kenneth
>
> ****************************************
> Kenneth E. Graap
> IBM Certified Specialist 
> i5 Professional System Administrator
> NW Natural (Gas Services)
> keg@xxxxxxxxxxxxx
> Phone: 503-226-4211 x5537
> FAX:    503-721-2518
> ****************************************
>
> -----Original Message-----
>
> An anonymous reader writes with the technique of Nolisting, which fights
> spam by specifying a primary MX that is always unavailable. The page is
> an
> extensive FAQ and how-to guide that addressed the objections I
> immediately
> came up with. 
>
> http://www.joreybump.com/code/howto/nolisting.html
>
> >From the article: 
>
> "It has been observed that when a domain has both a primary (high
> priority,
> low number) and a secondary (low priority, high number) MX record
> configured
> in DNS, overall SMTP connections will decrease when the primary MX is
> unavailable. This decrease is unexpected because RFC 2821 (Simple Mail
> Transfer Protocol) specifies that a client MUST try and retry each MX
> address in order, and SHOULD try at least two addresses. It turns out
> that
> nearly all violators of this specification exist for the purpose of
> sending
> spam or viruses. Nolisting takes advantage of this behavior by
> configuring a
> domain's primary MX record to use an IP address that does not have an
> active
> service listening on SMTP port 25. RFC-compliant clients will retry
> delivery
> to the secondary MX, which is configured to serve the role normally
> performed by the primary MX)."
>
>
>
>
>