[Coco] Re: [Color Computer] Re: OFF TOPIC! by golly..(spam)

[Lawrence Weeks]

Once upon a time (Sat Feb 25), KnudsenMJ at aol.com wrote:

> In a message dated 2/23/06 5:11:20 PM Eastern Standard Time,  gene.heskett at verizon.net writes:

>> I know of more than one mail server that imposes a 30 second delay
>> in the connect, and only if they try again after that 30 seconds
>> has expired will the message be accepted for delivery.

> Cool, but how do legit emailers deal with this delay? If they try
> again 5 or 10 minutes later, does this count as the re-try or as
> a new attempt, starting the cycle all over again? --Mike K.

This is called greylisting. It uses valid SMTP features to cut down
on spam. When you (your mail server) connects to another mail server
to attempt delivery, the the receiving server tells your end that
there has been a temporary failure -- try again later. Then your mail
server will, if it is implemented correctly, requeue the message for
delivery and try again later. The length of time between retries is
not specified by the recipient server. The sending server typically
has a fixed interval between attempts to process the outbound mail
queue. Thus the delay in delivering email with this scheme varies
widely. Most servers that implement greylisting will add a sending
server to a whitelist to bypass the greylisting, once it has passed
the gauntlet once.

Any properly implemented SMTP mail server will handle this just
fine. However, spam delivery software apparently does not handle the
SMTP temporary failure status code. Thus, that spam software never
retries delivery. This is just a temporary weapon against spam -- the
spammers are, and will, update their software to retry delivery. The
spam software in question is typically that installed on hijacked
Windows PCs by trojans/viruses/worms. As greylisting becomes more
and more common, its effectiveness will disappear.

If you use Postfix, you can install the postgrey or policyd package
to implement greylisting. The policyd software has many additional
features to cut down on spam without content filtering.

Larry
-- 
Lawrence Weeks                                    lweeks at anabasis.net
Anabasis Consulting Ltd