Custom exim filter for subject

Hi.

I'm lookinf for create a owned rule for fail email with any subject.

I see doc for How to create a custom Exim system filter file

But i don't see the way for this. I'm confused.

• do I need create a clon copy of /etc/cpanel_exim_system_filter or use my own empty file?
• Where i see doc for variables uses such subject header, etc... ?

I've create a custom file and config exim for use.

But i not sure it's correct 100%

Code:

 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#                                                                                                               #
#  Only process once                                                                                            #
#                                                                                                               #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
if not first_delivery
then
  finish
endif
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#                                                                                                               #
#  Ignore "real" errors                                                                                         #
#                                                                                                               #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
if error_message and $header_from: contains "Mailer-Daemon@"
then
  finish
endif
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #

###
if ("$h_subject:" contains "carta certificada no entregada a usted")
    then fail
endif