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Certain emails appear with non-standard fonts in headers

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  • 1 有這個問題
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Lately, I've been receiving a few "spam" emails where the text of the message headers ("From" and "Subject", in particular) appears in a non-standard font (e.g. different from all other plaintext in Thunderbird). I didn't think such a thing was even possible within email headers.

Looking at the message source (Ctrl-U), it appears the "From" and "Subject" headers are being encoded in UTF-8.

Is this some kind of attempt by the sender to bypass or trick anti-spam filters?

Note: attached pic has the text highlighted in yellow.

Lately, I've been receiving a few "spam" emails where the text of the message headers ("From" and "Subject", in particular) appears in a non-standard font (e.g. different from all other plaintext in Thunderbird). I didn't think such a thing was even possible within email headers. Looking at the message source (Ctrl-U), it appears the "From" and "Subject" headers are being encoded in UTF-8. Is this some kind of attempt by the sender to bypass or trick anti-spam filters? Note: attached pic has the text highlighted in yellow.
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Yes, UTF-8 can be used in subject lines, and yes, it can make some spam filtering harder work.

The legitimate intention is to allow non-Latin character sets to be used in subject lines and addresses. One minor form of abuse (IMHO) is using it to insert icons into subject lines. This is a typical example, from a travel company who use it to insert a calendar icon into the subject line.

Subject: =?UTF-8?B?8J+ThSBDaHJpcywgaXMgaXQgdGltZSBmb3IgeW91ciBuZXh0IHRyaXA/?=

As a side effect, it's now non-trivial to tell what the message is about, at least when looking at the source.

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