On Wed, Jan 28, 2026 at 06:03:06PM +0100, Michiel Hazelhof via Postfix-users
wrote:
> Now let's send another email where the subject contains
> "RandomStringToKeepEverythingFunctioning`MoreText", will pass the filter,
> the left single quotation mark (U+2018) will make the email bypass all
> regex/pcre filters.
Subjects with non-ASCII characters are encoded per RFC2047, possibly
entirely in base64. For example, when I compose a message with
subject:
$ perl -C7 -e 'printf qq{foo\x{2018}bar\n}'
foo‘bar
The resulting RFC5322 message has for a subject header:
Subject: =?utf-8?B?Zm9v4oCYYmFy?=
this is unsurprisingly not matched by:
/^Subject: foo/
Postfix header_checks DO NOT do RFC2047 decoding, you need
a content_filter or milter for that.
--
Viktor. 🇺🇦 Слава Україні!
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