Martin Geisler Online

… we’re ready to go! Tra-lala-lala! :-) It’s the middle of the night and Stéphanie and I are ready to go back to Denmark. We’ll take the train from Aarau at five o’clock heading for Zürich and then fly to Copenhagen at seven — in the morning that is!

There we’ll go to the big U2 Vertigo concert in Parken — I’ve been listening to their music the last couple of days so that I can be well prepared :-)

I’ll be going to Aalborg after the concert to visit my family, and later I’ll go to Århus to visit all the guys (and girls) at Skejbygård and DAIMI (that will be guys only…). I’m really looking forward to it!

Just when I thought that I had solved my mail problems the next problem appears: the addresses that Bluewin gives out to its ADSL customers (like Stéphanie and I…) are blocked by MAPS! Aargh!

So now I cannot send mail to any SMTP server which consults the Dynamic User List (DUL) — and so having a private SMTP server is no longer an option. Sending my mail through Bluewin isn’t that good either, considering the problems I had sending mail to SourceForge.

I’ve now complained to Bluewin and I hope they can either fix their SMTP server (or at least explain where my mail went…) or remove their IP addresses from DUL. They’re the only one who can get the IPs removed from DUL, us users cannot do anything. I find this very annoying since my server has never been sending out spam and it has never been configured as an open relay.

Oh, and look at the little stamp-sized window you get to write in when you want to contact the Bluewin customer service:

Do they really think that they will receive fewer complaints just because they make the text-area smaller?

We visited the Moon for the first time on July 20th 1969 — exactly 36 years ago today. I still think we should go there again! Until NASA gets their act together you can visit Google Moon and look around :-)

I spend some time today trying to figure out how I would be able to send mail to SourceForge. SourceForge is an enormous enterprise with more than a million users and hundred thousand projects, most of which have one or more mailinglists associated with them — the amount of mail flowing through SourceForge each day must be huge. So why should I have difficulties sending mail to an address at SourceForge, you might ask? I’ll tell you… :-)

First I discovered that mail bound for mailinglists at SourceForge would disappear on its way. The mail first goes to my local Exim which forwards it to mail.bluewin.ch — the SMTP server at my ISP Bluewin. After that I have no idea what has happened to my mail, I only know that it doesn’t reach the SF mailinglists. A mail to postmaster@bluewin.ch six days ago has gone unanswered… :-/

I then tried cutting out the middle-man and configured my Exim (using the super-simple Debian way of dpkg-reconfigure exim4-config) to send its mail directly like a full-blown SMTP server. I had initially not configured Exim like that because I didn’t want to add yet another publicly accessible server to my system.

But then I ran into the next problem: the spam filtering done at SourceForge. Every time someone tries to send something to their Exim SMTP server (cool, SourceForge use Exim too!) it will make a callout verification of the sender address. This simply means that it will try to deliver a message to the envelope address in the mail. In my case that failed for some reason, and I got this in my Exim log file:

451-could not connect to xxx [xxx.xxx.xxx.xxx]: Connection refused
451-Could not complete sender verify callout for <mg@xxx>.
451-The mail server(s) for the domain may be temporarily unreachable, or
451-they may be permanently unreachable from this server. In the latter case,
451-you need to change the address or create an MX record for its domain
451-if it is supposed to be generally accessible from the Internet.
451 Talk to your mail administrator for details.

I tried opening my router to allow the incoming connection to port 25 (SMTP) but it didn’t help. What to do? The usual when you run into a problem like this: read lots of man pages, configuration files, documentation, websites, etc… :-)

And surely enough, it worked: While reading through the Exim configuration files under /etc/exim4/conf.d/ I stumbled over a reference to /etc/email-addresses. That file is used by Exim when it inserts the envelope sender header in its outgoing mail: if a user is not listed in that file (the default) then it generates the envelope address of

Return-Path: <username@hostname>

In my case that made SourceForge do the callout back to my machine. If I instead add the line

mg: [email protected]

to /etc/email-addresses I get the following, much better envelope address in my outgoing mail:

Return-Path: <[email protected]>

which causes SourceForge to check with mail.mgeisler.net (the mail exchange for mgeisler.net). And this check succeeds! Hurray, I can now once again send mail to SourceForge hosted mailinglists!

By the way, if you’re running an SMTP server and you’re having problems with spam, then try the Spam Filtering for Mail Exchangers guide to rejecting junk mail in incoming SMTP transactions. They describe a whole bunch of tricks, including the callout verification technique described above and the very clever greylisting technique.

The advantage of this is that you’ll save yourself the trouble of filtering the spam later using something like SpamAssassin, and you’ll save yourself the bandwidth cost of receiving the spam in the first case since you can drop the connection before it has even entered your system.

I just came across Top 10 tech we miss at CNET.com, who are currently celebrating their ten year anniversary. They have put manned space exploration at the top of the list, and I think they’re right.

We first landed on the Moon on July 20, 1969 with the Apollo 11 mission. The launch of the Saturn V rocket is shown in the first image on the right. The second image shows Buzz Aldrin as he descends ladder from the Lunar Module, also on the Apollo 11 mission. The Apollo 17 mission was the last mission to carry men to the Moon and it returned to Earth on December 19th, 1972. The Command Module is shown just before splashdown in the third image on the right. Click on either image to get a high-resolution version from NASA. Crop and resize them a bit and they make perfect backgrounds!

So the age of exploring the moon lasted just over three and a half years and in the last 33 years no man has set foot on an extraterrestrial world.

I think that’s a shame! We once had the technology to go to the Moon, but now it’s gone. But what’s worse: we have lost over thirty years of potential experience. If the Apollo missions had continued would we then have a base on the Moon now? On Mars? Nobody knows, but I feel that we’re not going to get those things if we keep flying around in near Earth orbit all the time.

I would love to see humans on Mars, our new Frontier. When I see films and documentaries from the space race in the sixties I always envy the people who lived to see the first man on the Moon. I would really like to be able to tell my children or grandchildren that I saw the first man (or woman) on Mars.

I’m also the optimistic (idealistic even?) type of person who thinks that exploring and pushing the limits of what we know and what we can. Spending money on advancing science would be a much better way to improve the conditions for future generations than, say, buying yet more military hardware.

Sure there are lots of problem on our own planet Earth — hunger, wars, diseases, and lots of other problems — but that doesn’t mean that we should constrain ourselves to solving those problems before we can look beyond to other worlds. (Wow, that was almost poetic, wasn’t it? :-)

By the way: all the beautiful images here are of course from NASA, more precisely the Apollo Image Gallery where you’ll find over 3000 original images from the Apollo missions. All images produced by NASA are without copyright — this applies to all material produced by US goverments. Very nice exception I say! (This exception also applies to stuff produced by an agency like the CIA: for example, data from the CIA World Factbook is used by Wikipedia.)