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Blocking Junk Fax Spam with Asterisk

We have a fax machine in our master bedroom (don't ask), and eventually the fax spammers got ahold of the phone number. Pretty soon the middle of the night beeps and noises became intolerable, and I began to look around for a solution. Junkbusters has tons of great advice for taking legal action against the criminals sending this crap, but I don't have the time to do this, unlike, say Steve Kirsch.

Looking for a quick technical solution (ok so everything looks like a nail to me), I developed a simple, but pretty effective approach using Asterisk. Asterisk is a telephony server that I already run in our home, handling things like long-distance least-cost routing, and so on — basically I'm using it as a IP-PBX. It's also wonderfully programmable, and has a decent 3rd party soft fax addition.

Now when we get a fax call, Asterisk picks up the line and check for caller-ID. If available, and the number isn't in a blacklist (or is in the whitelist), then the fax goes to our fax machine. If there's no caller-ID, then Asterisk plays the special information tone (SIT), then the fax goes to the soft fax, and then emailed to me (where it's usually deleted).

The SIT or "Tele-zapper" tones is the sound one gets before the familiar "we're sorry, that number..." when something is wrong with a call (at least in North America). This may help remove our phone number from the junk faxer's lists.

The results are quite good though not perfect. We've gone from about 1 fax per night, down to about 1 every couple of months.

Categories: technology

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