[exim] BCC filtering in system_filter.exim

Hello all,



I have an email alias staff@??? that contains all the staff member
email addresses of the company. However, only the company bosses
eric@??? and john@??? are allowed to send email to
staff@???.



I've setup a message filter in system wide filter (system_filter.exim) like
this:



## staff@??? restriction:

if $h_to:,$h_Cc: matches "staff@???" and ($h_from does not match
"eric|john@???") then

fail text "You are not allowed to send mail to this address"

endif



It works fine for rejecting normal staff members from sending messages to
staff@??? using TO or CC. However if a normal staff sends email to
staff@??? using BCC, my filter failed to work.



Is there a way to stop people sending to staff@??? using BCC?



Thank you.



Regards,
Will L