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Filter for Extended ASCII characters in spam mail

  • 3 replies
  • 2 have this problem
  • 1 view
  • Last reply by Zenos

Blacknest
Blacknest
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I've been getting an increasing number of spam mails that show up with strange characters in the subject line and gobbledegook in the body. If I look at the emails directly on my BTMail web page, the emails have an image instead of body text, featuring the usual sort of spam advertising. The (very limited) filters available on BTMail are useless. However, being an old-fashioned kind of guy, I don't normally use webmail - I use Thunderbird as an email client to organise and store all my mails locally. I'm hoping that I can set up filters in Thunderbird to filter out this sort of spam.

As you'll see in this screen shot, the subject lines - which are usually > 150 characters - have blocks of 3 non-ascii characters between each 'actual' letter (on webmail these characters disappear, and the headings appear as ' Your horoscope..' etc).

Any suggestions as to how I can trap these?

BTW, the body text always appears to start with the characters "qéíz¶¡­ç†" but for some reason a filter trying to match this in the body of the message doesn't work either.

I've been getting an increasing number of spam mails that show up with strange characters in the subject line and gobbledegook in the body. If I look at the emails directly on my BTMail web page, the emails have an image instead of body text, featuring the usual sort of spam advertising. The (very limited) filters available on BTMail are useless. However, being an old-fashioned kind of guy, I don't normally use webmail - I use Thunderbird as an email client to organise and store all my mails locally. I'm hoping that I can set up filters in Thunderbird to filter out this sort of spam. As you'll see in this screen shot, the subject lines - which are usually > 150 characters - have blocks of 3 non-ascii characters between each 'actual' letter (on webmail these characters disappear, and the headings appear as ' Your horoscope..' etc). Any suggestions as to how I can trap these? BTW, the body text always appears to start with the characters "qéíz¶¡­ç†" but for some reason a filter trying to match this in the body of the message doesn't work either.
Attached screenshots

All Replies (3)

Matt
Matt
  • Moderator
  • Top 10 Contributor
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The issue is one of character sets. have a look at what is specified in these mails. My guess is it will be something odd.

Blacknest
Blacknest Question owner
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I'm assuming that the non-ASCII characters are being encoded by the mailing software with Base64 encoding, as the subject line starts with:

Subject: =?UTF-8?B?

However, I'm not sure how knowing this helps me trap the mails, as I can't find a way to put non-ASCII characters into a filter.

Zenos
Zenos
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Sometimes it's easier to go at if from the other end. The FiltaQuilla add-on would let you use a regular expression to define a range of acceptable characters, and you could use it to reject any messages containing characters outside that range.

Simplistically, limiting it to characters 0 to 255 would allow all the standard ASCII symbols used in English.