[Greylist-users] Time to resend a message
raeburn at raeburn.org
Tue Jul 5 02:37:12 PDT 2005
On Jul 5, 2005, at 04:41, Matthias Haeker wrote:
> there is a ongoing discussion on how to understand the resending time
> in that a message shoud be resend after beeing rejectet with a lets
> 450: ...........( Greylistet for 300 sec)
> must i resend **within** the 300sec or earlyest after the 300sec.
The basic idea of greylisting is that the sending site should queue up
messages on a temporary error (the 450 error code), and retry
periodically for some amount of time, where the delay between tries and
the amount of time before the sender finally gives up should be
"reasonable". What "reasonable" means varies, of course, but usually a
site will retry anywhere from every 15 minutes to once every few hours,
and will keep trying for at least 3-4 days, maybe a week.
However, for legitimate mail, this does introduce a delay. (There's a
lot more to it, where typically you keep track of who's tried to send
mail from what addresses before, and if the sending mailer does retry
the mail, then in the future, at least for a while, you accept the mail
Greylisting tends to win, because most spamming software doesn't retry
at all, and if it does, it usually retries immediately, several times,
and then gives up. So retry attempts within the first very short
period of time are still given the temporary failure code; this is
probably what the "300 sec" refers to -- your mailer should make
another attempt after 5 minutes, and the mail should get through. But
if you're using a typical mailer configuration, you probably are using
"reasonable" values, and the mail should eventually go through. Resend
attempts within the 5 minute window shouldn't be a problem, though;
they'll just get more temporary failure indications and stay in your
> please excouse if ther is already a thread in your mailing list
> regarding t=
> his question.
> i am not a greylist user, the companys i am the admin from dont send
> any sp=
> am and i have not the time to leran everything
> about all new "ANTISPAM" solutions.
> but we are realy troubled to send valid genuine email to customer
> using gre=
You don't say whether the mail is actually getting through, in the end.
But if your site and the site using greylisting are configured
reasonably normally, it should be nothing worse than delaying the
initial messages between parties (specifically, SMTP envelope
addresses) at your two sites who haven't talked before (at least,
There are some mail handling techniques that can cause problems when a
site is using greylisting, though:
* VERP -- variable envelope return path addresses, often but not
always in mailing lists, where the SMTP sender has a form that may look
something like "<ListName>-<MessageNumber>-<Recipient>@hostingsite.com"
and is different for every message.
* sending server pools -- If one sending attempt comes from one IP
address, and the next attempt comes from a different IP address, the
typical greylisting implementation will not see them as related, and
would treat both of them as first contacts from different potential
spammer sites, returning temporary failures and waiting to see if
either attempts to resend (from the same address). Usually, there's a
timeout on how long a site can wait before resending before the
greylist implementation throws away the data -- if you don't retry
within some "reasonable" time, it assumes you probably were a spammer
and gave up, so it forgets about you. Because of this, if you've got a
large sending pool, and/or don't retry very often, the greylist
database record for one of your sending servers might be discarded
before that server gets around to trying to send the message again.
In the worst case, you can try to contact the postmaster at the site
you're having trouble with, and see if either they're doing something
wrong, or they think you're doing something wrong, or whatever else
might be amiss, and you can work together to fix it. (You might also
suggest to them that in the SMTP message they send back, since it looks
like they're trying to make it informative, they could include a URL
for a web page explaining things a little better.)
I hope this helps....
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