How to block email from a specific address on a cPanel/WHM or other web server using Exim

With EXIM, you can setup filters that can perform a large number of tasks, like blocking message, or blind copying messages to other email addresses.  In this case, I’m going to create a filter to cause an email coming from a specific sender to fail (the email address I use to send the email in PHP). What you’ll want to do is find your System Filter File for EXIM.  In WHM, you can find this file listed in your EXIM Configuration Editor about half way down the page. Once you’ve located the file, log into SSH and edit the file.

pico /path/to/your/file

Then enter the following filter into the file and save it:

if first_delivery
and ( ("$h_from:" contains "emailtoblock@mydomain.com")
)
then fail
endif

If you’d like a copy of the email sent to you after the message fails so you can make sure it is correctly formatted, just add one line:

if first_delivery
and ( ("$h_from:" contains "emailtoblock@mydomain.com")
)
then
unseen deliver "youremail@yourdomain.com"
fail
endif

I suggest you read up more about EXIM filtering for more advanced functions. Where I Learned This: I found the solution the Imthiaz Blog and the Exim Documentation.

Exim Configuration Manager:basic editor

There will be a warning in Filter configuration File: /etc/cpanel_exim_system_filter

Exim filter
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#  cPanel System Filter for EXIM                                                                                #
#  VERSION = 2.0                                                                                                #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!DO NOT MODIFY THIS FILE DIRECTLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!      #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#   Direct modifications to the /etc/cpanel_exim_system_filter file will be lost when the configuration is      #
#   next rebuilt. To have modifications retained, please use one of the following options:                      #
#                                                                                                               #
#    1)                                                                                                         #
#      * Place each sysfilter block you wish to include in a unique file at:                                    #
#            /usr/local/cpanel/etc/exim/sysfilter/options/                                                      #
#      * Enable or disable the custom block in WHM using:                                                       #
#          Service Configuration => Exim Configuration Manager => Filters => Custom Filter: [your unique file]  #
#                                                                                                               #
#    2)                                                                                                         #
#      * Create a custom sysfilter file in /etc/                                                                #
#      * Change the location of the sysfilter file in WHM using:                                                #
#          Service Configuration => Exim Configuration Manager => Filters => System Filter File                 #
#                                                                                                               #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!DO NOT MODIFY THIS FILE DIRECTLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!      #
# # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
#                                                                                                               #
#  Only process once                                                                                            #
#                                                                                                               #
# # # # # # # # # # # # # # # # # # # # #

So I created this simple php file on /usr/local/cpanel/etc/exim/sysfilter/options and it was visible in the WHM filter.