Messages to Python-List aren't posting

[Steven D'Aprano]

On Fri, 19 Jul 2013 09:57:47 -0500, Skip Montanaro wrote:

>> Is it possible that the name "Matthew Lefavor" has been added to a
>> greylist or something?
> 
> That's not how greylisting works.  Greylisting is a scheme used to
> eliminate spam.  The server knows what email addresses it's received
> mail from in the last little while (say, the last month).  When it gets
> a message purporting to be from someone not in its little database (say,
> user at somewhere.com) it responds with a "try later" message.  Legitimate
> mail will be delayed for a few minutes.  The sending SMTP server will
> try again, and the message will be accepted by the receiving server.
> That server will also record user at somewhere.com as a "known" address. 
> The theory behind greylisting is that a spambot either won't come back
> and retry sending (it's going millions of messages to flood the net
> with, and can't be bothered to retry mail) or will be found and shut off
> by ISPs before the delay period expires.


Greylisting is great, but there are a couple of quirks, as the company I 
work for discovered the hard way. Some ISPs don't follow the rules. I'm 
not talking about dinky little ISPs run by some guy in a basement, I'm 
talking some of the biggest ISPs in Australia like Optus or Bigpond. They 
either completely ignore the "try later" message, and report it as a hard 
failure, or they wait a full day before trying again instead of a few 
minutes. Or, if they do try again, they try again from a different mail 
server, so the greylisting software sees a different sender/server 
combination, and greylists that as well.

Admittedly, this was a few years back that we ran into this problem, and 
since then we've just routinely whitelisted email from Optus and Bigpond, 
curse their black souls for making spam prevention just that little bit 
harder. So I suppose it's possible that they've stopped being bad actors 
and started following the standards correctly.

No really, stop laughing, it is technically possible.



-- 
Steven