> It seems to be the extension "regex". In the exim-documentation "Chapter > 2 - Sieve filter" I found the following sentence:
>
> "The Exim Sieve implementation offers the core as defined by RFC 3028,
> comparison tests, the subaddress parameter, the copy, envelope,
> fileinto, notify, and vacation extensions, but not the reject extension."
>
> The list doesn't include "regex", so is it true, that it won't work? Is
> there a way to make it work? Or what else can we do?
You got it right, "regex" is not implemented. This extension introduces
variables, which requires a large amount of work to implement, and worse,
regular expressions potentially may cost quite some CPU time if not
used sensibly.
Since it makes sense to allow users to set arbitrary scripts, including
e.g. the example you gave, many admins favour not to couple system
availability to the belief that nobody would configure a script causing
sudden CPU time demands.
