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28/01/2019: Spam messages still getting through despite your filter?

In recent conversations I have often been asked why setting spam filters to block messages containing specific words or phrases in customers' email clients has not been effective.

In short, and to save having the same conversation over and over again, here is a summary of my response…

To prevent deletion of their junk mail by mail filters and spam traps, spammers go to great lengths to obfuscate the phrases or words in their message that would give away their true purpose. The image in this article compares the text that is displayed in a message window with the underlying code used to create it. Compare that to the user and code views of a genuine email in the additional images. Apart from the fact that I have mis-spelled Barney Rubble's name, this message shows no signs of being illegible to humans or spam filters.

Another way that spammers try to make sure their messages get delivered include 'spoofing' the recipient's own address as the sender. This is ridiculously easy to do and almost impossible to prevent. There is so much written about this online that it is not worth repeating here, simply searching for the topic will reveal a wealth of information. The thinking behind this is most likely that all of us at some time or another will 'whitelist' our own address so that we can make sure we receive emails from ourselves.

As the online spam filter in Apache SpamAssassin is based on a numeric evaluation of contributing factors, some spammers have evolved techniques of falsifying the spam score to a ludicrously low negative number. For example, Apache SpamAssassin by default quarantines every message with a score of 5 or more, whereas most of the messages in one particular category of scam have faked scores of -800 or more.

So, what can we do to cut down the torrent of spam? Taking the common sense precautions that have been outlined here in previous articles is going to help, as is installing and maintaining a rigorous spam filter on your local machine. However, if you are still being plagued by these messages using obfuscation techniques, we can implement a number of measures at server level for you. This will protect all the devices you use for managing emails and should last for some time before the next technological breakthrough on the part of the spammers, hackers and malware distributors makes an update necessary.

If you have any questions, please don't hesitate to call or click in the header of any page to send an email.

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