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aaron311

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Lately I've been getting a good amount of spam with pdf / jpeg attachments between 150kb to 350kb in size. Apparently, SpamAssassin wont scan these messages, and my custom rules don't appear to work either (although Kerio support claims they do).

Is there a way to force Kerio / SpamAssassin to scan messages with attachments?

Thanks!
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sgongola

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AFAIK Spamassassin examines text. Using OCR to retrieve text from a graphic requires greater processing power than is usually available for continuous incoming emails and is outside the scope of what spamassassin does. However, the presence of graphics in emails does affect the spamassassin score.

Much of the same may be true for scanning PDF attachments and any mimed attachment but I am not exactly sure about that.

Spam is supposed to attract your immediate attention. This happens with text, html, and pictures. This is not true for pdf where you need to be convinced to invoke an external reader so the need for scanning pdf is not as great.
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aaron311

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Honestly, I don't really want SpamAssassin (or Kerio) to scan the individual attachments. I'd rather Kerio would scan the message just like any other email. There may not be text in the body of the message for SpamAssassin to scan, but doesn't it also take the subject and headers into consideration when giving a score?

So basically all spammers have to do is attach a picture or any other file to the message, and Kerio will deliver it as if it were white listed. I think they've figured this out, because my level of spam getting through is getting larger by the day.
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sgongola

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The presence of a graphic attachment does affect the spam score. So does the presence of a graphic with no other information. Neither acts as a "white list".
You should also be using other facilities in "content filter">>"spam filter". They are all important. spamassassin, Spam rating and custom rules handle email that has entered your system. The others prevent messages from getting into the system in the first place. They reduce the processing load on your email server and they probably prevent emails from getting in that spamassassin might not recognize as spam.

[Updated on: Thu, 30 April 2009 18:59]

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Vink

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aaron311 wrote on Thu, 30 April 2009 18:30

Honestly, I don't really want SpamAssassin (or Kerio) to scan the individual attachments. I'd rather Kerio would scan the message just like any other email. There may not be text in the body of the message for SpamAssassin to scan, but doesn't it also take the subject and headers into consideration when giving a score?

So basically all spammers have to do is attach a picture or any other file to the message, and Kerio will deliver it as if it were white listed. I think they've figured this out, because my level of spam getting through is getting larger by the day.

SpamAssassin scans all messages, but headers alone might not be enough for SA to classify a message as spam. For header recognition you should introduce using blacklists (spamfilter, 2nd tab). From my experience (1 domain with 130 users) you can safely add SpamCop and SpamHaus to simply block positives.
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