It is indeed a "poor mans greylisting". Real greylisting is however much 
more effective. Reasonably large amounts of spam is targeted directly at 
the backup mailserver and will come through.

It doesn't seem have the drawback that greylisting has: possible large 
delays. But it did make me think of a possible solution for that in 
greylisting. What if you would have primary and secondary MX point to 
two different IP's on the same host. Both IP's do accept mail and run 
the same greylisting filter.
Currently, greylisting will only start accepting mail from one sender if 
it retries (for example) 15 or more minutes after the first attempt. And 
MTA's can take much longer before doing a second attempt on the same MX.
With both MX's pointing to one machine (two IP's), we could instruct 
Greylisting to accept mails without delay if we have first seen an 
attempt on the primary IP, and now get one on the sencondary. 
XMailserver has a *LOCALADDR-variable that will help with this.*
If the information on that site is correct, then most MTA's would retry 
on the second MX almost instantly after trying on the first one. So 
there basically is hardly any delay.

Do take into account that the delay does also has its benefits. Spam 
that is delayed, is more likely  to be captured by an other filter 
(blacklist, Pyzor, Razor, DCC, ...).

Any thoughts?

Sincerely,
Bart Mortelmans



Filip Supera wrote:
> Hello,
>
> Just heard about this in the Spamtools mailing list :
>
> http://www.joreybump.com/code/howto/nolisting.html
>
> Any thought ?
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