Spam Filtering 060

I've recently been re-working the way I receive email due to issues with my ISP. After my first re-org, I inadvertently found myself getting less spam.

I say "Spam Filtering 060" as opposed to 101, as these techniques are super-basic and wouldn't even qualify for college credit.

This may sound funny, but I want to get as much junk mail as possible. I constantly need to keep feeding "the butcher" in order to make sure it catches as much as possible. I can't train the SpamButcher spam program to catch stuff that I'm never exposed to.

So, even if you're setup for "no filtering" with your ISP, it turns out they're still probably doing a few things to prevent certain messages from getting to you. Most of these things are pretty reasonable.

First, if the message is from a domain that doesn't exist, it's probably going to get blocked. If the email server does a quick lookup and determines that fjfjfjwaaaaa.com is not even registered, it won't accept email from it.

Some servers take the next logical step and require the sending domain really have a valid MX record in DNS. This is to say, the domain must be capable of receiving email. Both these items make a lot of sense.

. Another common trick is to perform a reverse-DNS lookup on all connecting IP addresses. If an IP address doesn't have valid reverse DNS entry, it indicates a possible dynamic address that probably shouldn't be sending email directly to SMTP servers.

Some servers utilize other more advanced techniques, even if users explicitly disable filtering. Some of these method present problems with false-positives. These will be covered in another article.

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