4.40.5: IPBlock 451 versus 550

Rakesh rakesh at NETCORE.CO.IN
Thu Mar 17 13:00:35 GMT 2005

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Jeff A. Earickson wrote:

> Julian,
> Just curious as to why you changed IPBlock from fatal rejections
> to tmpfail.  I've had a couple of spammers pounding on my system
> with crap that would have ordinarily been booted by IPBlock for
> good.  Now they just keep trying.  I've modified my copy of
> CustomConfig.pm in 4.40.5 to do the 550 rejections again.

my idea of suggesting Jules for 451 error instead of 550 error code was
that, unknowingly we do not bounce back some geniune mails just because
the sending server is sending too many mails to us. For e.g. a yahoo's
outgoing server might be sending quite a good amount of mails to an MX
server hosting many domains. So if we just temporarily deny from
accepting the mail then however i am quaranteed that a good outgoing
server would definitely try again for delivery which won't be applicable
incase of a 550 rejection and probably some sending out an important
mail would finally get a bounce back for no good reason. This totally
different from the greylisting concept in which any server initiating a
first time connections will have to compulsarily try again later.

However majority spammers use hijacked machines or poor SMTP engines to
send out spams and asking them to try again later with 451 error code
wouldnt be of any harm as they don't bother to try again later so the
spams doesn't come at all. However if they are using someone else's
server which actually does retry sending the spam, then we can probably
notify the administrator to checkout his system or atleast have 1 hour
to block the IP on the firewall.

Rakesh B. Pal
Emergic CleanMail Team.
Netcore Solutions Pvt. Ltd.

"First they ignore you. Then they laugh at you.
Then they fight you. Then you win."
                                                - M. Gandhi

Netcore Solutions Pvt. Ltd.
Website:  http://www.netcore.co.in
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