Slightly OT: Greylisting success or failure stories?
Scot L. Harris
webid at cfl.rr.com
Fri Feb 4 02:31:13 UTC 2005
On Thu, 2005-02-03 at 21:12, Jeff Kinz wrote:
> On Thu, Feb 03, 2005 at 09:03:24PM -0500, Scot L. Harris wrote:
> > On Thu, 2005-02-03 at 20:34, Jeff Kinz wrote:
> > >
> > > It is inadvisable for anyone using email in a professional capacity
> > > to use any form of TMDA (whitelisting/greylisting).
> >
> > Interesting rant. And I agree with most of what you state about TMDA.
> > I refuse to respond to such requests.
> >
> > However don't lump greylisting in with TMDA.
>
> Point taken. The exact definitions of what constitutes "whitelisting,"
> TMDA and greylisting have shifted continuously since their recent rise
> in popularity.
>
> But -according to a Google definition lookup - You are right.
> Greylisting is not a form of TMDA. Quote:
> ############################################################
>
> Greylisting
> How it Works
<snip> Good explanation of how greylisting works. :)
>
>
> This leaves the possible remaining objection centered around exactly
> how long the email will possibly be delayed for, and/or the possibility
> that some email systems mail never retry. (poor ones ;-) )
>
I have seen very little difference between setting a 30 minute or a 2
minute greylisting delay. Other than starting with a 30 minute delay of
course. :)
Of course the actual delay is controlled by how the sending MTA queues
and retries messages. Based on the log files I have looked at most
legit MTAs retry a message several times in the first 5 to 10 minutes.
MTAs that don't comply with the RFCs should be identified and removed
from the Internet. If they don't respond correctly to a temp failure
code then they are subject to loosing email in other situations as well.
Probably the biggest problem is identifying server farms where a message
may be retried from a different IP address. The greylisting
implementations I have seen generally start with a list of such servers
which are whitelisted and as such are not greylisted on the first
transmission.
--
Scot L. Harris
webid at cfl.rr.com
Quantity is no substitute for quality, but its the only one we've got.
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