The Boston Diaries

The ongoing saga of a programmer who doesn't live in Boston, nor does he even like Boston, but yet named his weblog/journal “The Boston Diaries.”

Go figure.

Tuesday, September 11, 2007

Note on a greylist implementation

For such a simple concept, greylisting has a lot of pitfalls. I managed purely by chance to see that Mark had sent me an email (I saw the tuple in the log files). Curious to see how long it took to be accepted, I was horrified to see that not only had it not been accepted by the greylist daemon, but that it had been kicking around the system for over 30 hours!

Like clockwork, Mark's email server was attempting to send the message every thirty minutes, on the dot, and thus, was never getting through the embargo time out. It all came down to this one piece of code:

if (difftime(req->now,stored->atime) < c_timeout_embargo)
{
  stored->atime = req->now;
  send_reply(req,CMD_GRAYLIST_RESP,GRAYLIST_LATER);
  return;
}

If the last access time was less than the embargo timeout, update the access time and send back “try again later.” At the time I found this out, I simply added Mark's server IP to the whitelist and restarted the greylist daemon.

Later, at the weekly Company meeting, I mentioned some of the issues I've had over the week and after some discussion, I made two changes to the greylist daemon:

  1. cut the embargo timeout from one hour to 25 minutes
  2. use only the sender and recipient in the tuple, dropping the IP address (or rather, ignoring it)

To test these changes, I also removed a bunch of the whitelisted IP addresses, to test the effectiveness.

They weren't all that effective.

I had problems with BellSouth, trying to deliver an email for four hours (and, as always, well below the embargo threshhold). I restarted the greylist daemon with an extended whitelist of IP addresses.

In reading many pages on greylisting, I realized I may have mis-interpreted the original whitepaper:

With this data, we simply follow a basic rule, which is:

If we have never seen this triplet before, then refuse this delivery and any others that may come within a certain period of time with a temporary failure.

So instead of checking against the last access time, I should compare against the creation time of the record.

Off to make that change and see how it goes.

Constrained writing demoed via email exchange awhile ago

Cadaeic Cadenza (link via Jason Kottke) is a “constrained writing,” where the constraint is each word has the number of letters corresponding to a digit in π (first word has three letters, second word has one letter, third word has four letters, and so on).

It reminded me of an email exchange I had with my friend Hoade, wherein each email was constrained in some manner.

It starts with a reply to Hoade:

From
Sean Conner <spc@pineal.math.fau.edu>
To
Sean Hoade <shoade@sun1.iusb.edu>
Subject
Re: Scooby Dooby Doo, Where Are You?
Date
Mon, 19 Jun 95 22:56:45 EDT

A long long time ago in a network far far away, The Great Sean Hoade wrote:

Conman—

Hello. Hope you are well. I am fine. Good. Help. I can just make one-syllable words, 'cept for the word “syllable.”

Will try to keep this small. Can I count on you to come down here two months from now? I look towards the day you are here. And I think I can help you with your word choice. Too bad you had to use a long word there. It is not hard to avoid those words. See?

From
Sean Hoade <shoade@sun1.iusb.edu>
To
Sean Conner <spc@pineal.math.fau.edu>
Subject
cool
Date
Tue, 20 Jun 1995 17:27:19 -0500 (EST)

Harder, methinks, writing choices using only two-time counting …

From
Sean Conner <spc@pineal.math.fau.edu>
To
Sean Hoade <shoade@sun1.iusb.edu>
Subject
Re: cool
Date
Tue, 20 Jun 95 18:18:38 EDT

Truthful wisdom indeed. Thinking dual phonems (spelling?) isn't easy. Although practice ensures success. Agree?

(And yes, I still have problems speling)

From
Sean Hoade <shoade@sun1.iusb.edu>
To
Sean Conner <spc@pineal.math.fau.edu>
Subject
Re: cool
Date
Tue, 20 Jun 1995 20:06:21 -0500 (EST)

Sentence fragments? Forswear fragments, Conner! (Asshole …)

From
Sean Hoade <shoade@sun1.iusb.edu>
To
Sean Conner <spc@pineal.math.fau.edu>
Subject
Re: cool
Date
Wed, 21 Jun 1995 18:44:25 -0500 (EST)

Attempting tripartite syllabic collections challenges heartily, Connerman.

Personal opinion: redundant repeating selections crucify attempters thoroughly.

The constrained emails died down for a few days, until this exchange:

From
Sean Hoade <shoade@sun1.iusb.edu>
To
Sean Conner <spc@pineal.math.fau.edu>
Subject
Four syllables?
Date
Mon, 26 Jun 1995 23:22:30 -0500 (EST)

Enigmatic, mysterious communiques– incredible electronic correspondence!—solidify, obviously computerized benedictions Hoade-to-Conner.

Whaddyathink?

Hoade

P.S.—Aquarium!

From
Sean Conner <spc@pineal.math.fau.edu>
To
Sean Hoade <shoade@sun1.iusb.edu>
Subject
Re: Four syllables?
Date
Mon, 26 Jun 95 22:51:18 EDT

Incredible! Spectacular! Impressively unspeakable phenomenon! Untoppably quisicential!

Did I mention that I kant spel?

Anyway, a few months go by, and our last exchange of contrained emails:

From
Sean Hoade <shoade@sun1.iusb.edu>
To
Sean Conner <spc@pineal.math.fau.edu>
Subject
Re: Perfectly Prosaic Prose
Date
Sat, 27 Jan 1996 07:54:21 -0500 (EST)

And because computers drain everyone's future—good! Have I just kinda loose morals? No! Only pious, questioning rabbis say this (until vacuous women—Xanax—yawn zestlessly).

From
Sean Conner <spc@pineal.math.fau.edu>
To
Sean Hoade <shoade@sun1.iusb.edu>
Subject
Re: Perfectly Prosaic Prose
Date
Sun, 28 Jan 96 3:33:25 EST

Zounds! Your xiphoid women vanguard unilaterally try soldierly responses quickly. Personally, one needs many large Kaffirian juggernauts, instigating hectoring grandiose fanaticism. Egads! Damnation! Cabalists be aware!

Yeah, you try writing a twenty-six word paragraph in reverse alphabetical order and see how easy it is.

Granted, what we did wasn't as difficult as writing a work with letter counts based on π or a book without the letter “E” but that doesn't mean it was easy.

Obligatory Picture

[The future's so bright, I gotta wear shades]

Obligatory Contact Info

Obligatory Feeds

Obligatory Links

Obligatory Miscellaneous

You have my permission to link freely to any entry here. Go ahead, I won't bite. I promise.

The dates are the permanent links to that day's entries (or entry, if there is only one entry). The titles are the permanent links to that entry only. The format for the links are simple: Start with the base link for this site: https://boston.conman.org/, then add the date you are interested in, say 2000/08/01, so that would make the final URL:

https://boston.conman.org/2000/08/01

You can also specify the entire month by leaving off the day portion. You can even select an arbitrary portion of time.

You may also note subtle shading of the links and that's intentional: the “closer” the link is (relative to the page) the “brighter” it appears. It's an experiment in using color shading to denote the distance a link is from here. If you don't notice it, don't worry; it's not all that important.

It is assumed that every brand name, slogan, corporate name, symbol, design element, et cetera mentioned in these pages is a protected and/or trademarked entity, the sole property of its owner(s), and acknowledgement of this status is implied.

Copyright © 1999-2024 by Sean Conner. All Rights Reserved.