Re: weird. . .

From: PhotoGecko Austin <gecko@photogecko.com>
Subject: weird. . .
Date: Tue, 06 Apr 2004 22:42:05 -0500

> Here's an internet paths and protocols question. I'm mightily
> confounded by this. And confounded minds want to know:

There are multiple possibilities, but the most likely cause has to do
with queues... no, this has nothing to do with the timely topic of
British system (nor the possibility that the ISP's server is located
in a Mediterranean country).

So, your posting arrives at usask.ca server, and gets sent out for
list distribution. These are queued in the smtp (mail) server at
usask.ca. At this moment, your mail server may have some temporary
porblem and can't receive it right away. So your copy of underlivered
email remains in the queue until future attempt, which can occur at an
interval that varies with the server (it can be 5 minutes or a few
hours).

There are many kinds of temporary errors. The usask.ca server may not
be able to find the email server for photogecko.com (which is
NETSOLMAIL.NET, and the usask.ca server needs to find the IP address
of this server.). Or it may be able to find what the server is, but
can't really talk to the server, possibly because the network is
congested, the netsolmail.net server is too busy, or netsolmail.net
server is temporarily down.

Before the usask.ca server attempts a retry, new postings come in, get
queued and delivered. By that time, your server might have come back,
so those new postings got delivered right away, but your older posting
probably had to wait until next retry interval.

Incidentally, many spammers use purposely broken and incompetent email
servers to send out spams but they are not designed to receive bounced
errors, or to deal with temporarily errored messages (because these
will take too much resource). So a new anti-spam technique is to
respond to all incoming emails from previously unseen senders with a
temporary error for the first time and see if the sender's server
retries. This is called greylisting, and this seems a great idea, but
it turned out that a lot of ISP's use inadvertently broken,
incompetent and crappy server softwares that do not fully comply with
the internet standard protocols. So the problems accumulate and fight
against spams don't move forward by much. This great idea is
practically unused because of too many incompetent (though legitimate)
servers... (right, this paragraph is entirely parenthetical and has
nothing to do with your question.)

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)