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by: Bernard Teo

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Bernard Teo
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List of Categories : Database * Technology * Commentary * Singapore * Travel *

Mon 03 Jan 2005

I get a breakthrough

Category : Technology/spamblocks.txt

We know for a fact that some mail servers are rather picky. They will reject mail coming from a dynamically assigned IP address, or one without a domain name, or follow any some other rule.

I've been wondering why my mail from (which is on a dynamic IP address) sometimes get through to the people at Apple Singapore and sometimes they don't (when Apple's servers' decide that it could be spam).

It's puzzled me for over a year - i.e., what has changed in my configuration that makes those servers decide one way or the other, because obviously I want my mail to get through all the time.

I rebooted our server today and realised that I couldn't send mail out to Leon Chen at Apple anymore, even though I've been able to do so for months now. So something has changed.

I dug around and found the answer - it's the DNS server. I've been playing around with setting up a DNS server, on and off, over the year. Turning the DNS server off causes the mail to be bounced back from a picky server. Turning it back on gets the mail through.

If there is a DNS service running on our local network when the mail server starts up, it'll be able to correctly discover its own domain name. (Otherwise it knows itself as, say, roadsteadserver.local). Seems like, when it knows that it should be, it'll be able to send mail out to other servers without getting bounced. (Or some such explanation.)

I don't know if I really understand what is happening but the moral of the story is - it's good to be able to run your own DNS service.

I've got a version of Postfix Enabler (in Obj-C) that will work with the next revision of our favourite OS - except that it leaks memory. Lots of it, I'm sure, until I figure out how all these retain and release stuff works. (Mike Beam's article at O'Reilly is a great starting point.) It ought to be known as Postfix Configurator or something because it won't be doing much enabling anymore.

Posted at 5:31PM UTC | permalink

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