Wednesday, August 1, 2007

On the business end of a blacklist. Oh the hilarity.

I had planned to write about something else for my next blog entry, but life came back and bit me with another spam related episode. Next time, I promise, I'll do something interesting.

In the meantime, I've discovered that a) very few people actually use SPF to reject mail b) the SPF syntax looks simple, but is hard to get right, and c) there are still blacklists which routinely block whole /24 nets.

This morning I got a message from somebody I met at BSDCan in May, asking me to do something LinkedIn-related. Naturally, since I felt I needed some more details to do what this person wanted, I sent a short email message. That message got rejected,

SMTP error from remote mail server after MAIL FROM: SIZE=2240:
host []:
554 refused mailfrom because of SPF policy

which means that the SPF record IN TXT "v=spf1 ip4:
ip4: -all"

does not do what you think it does. Mail sent from was not let through.

OK, the checking tool at the OpenSPF site seem to agree with, and I seriously can not blame them for the choice to trust SPF absolutely.

At the moment it seems my listing each host name is what does the trick. Weird. Anyway, next up in my attempt to communicate with my overseas friend, I tried sending a message from instead. That bounced too, but for a slightly different reason:

SMTP error from remote mail server after RCPT TO::
host []:
553 Dynamic pool

If you look up the data for, you will find that valid mail from there gets sent mainly from, which is in the tiny /29 our ISP set aside for my home net when I told them I wanted a fixed IP address.

I'm not sure if the rest of the "ip=194.54.107.*" network is actually a pool of dynamically allocated addresses these days, but I do know is that has not been dynamically allocated for quite a number of years.

Going to the URL gave me this picture:

This really gives me no useful information at all. Except, of course, that at they think that putting entire /24 nets on their blacklist is useful. Some of us tend to disagree with that notion.

Anyway, I filled in the form with a terse but hopefully polite message, and clicked Submit.

I was rewarded with this message:

If I read this correctly, they think mail from is spam because BGNett or MTULink have not set up reverse lookup for OR because they think the entire /24 is dynamically allocated. OR somebody in that subnet may have sent spam at one time. I can only guess at the real reason, and repeat over and over that blocking entire subnets will give you a generous helping of false positives.

Nevermind that, the SPF record which made my mail from go through to my overseas friend included a:hostname.domain.tld for all allowed senders.

And in other news, the PF tutorial saw its visitor number 15000 since EuroBSDCon 2006 on Saturday, last count is 15220.

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