[exim] Exim regex limit length

I've been having no luck with a simple regex to match strings with 20 or less characters.


My idea is to block certain commonly used subjects to make phishing attempts:


Example:


Subject example: Unlock Your Account

discard    condition = ${if match{$header_subject:}{.\{0,20\}Unlock Your Account\$}}
                 logwrite = Rejected By SPAM - $header_subject - FROM: "$sender_address"

I try to match the rule with other types of subjects used to steal data, but not work. (Example America Alert: Unlock Your Account)