A common request we get is how a user can automatically BCC outgoing email to another address. This is most often requested by law firms that need to be able to retain copies of communication. Forwarding incoming email is easy – there’s already a section in cPanel for it. However, if you want to forward outgoing email there’s a small twist.

First, go to WHM > Exim Configuration Editor, then click “Advanced Editor” at the bottom. Don’t make any changes, just click “save”. This should create a file on the server called /etc/exim.conf.local. From command line as root, you’ll need to edit /etc/exim.conf.local and add some options to the @CONFIG@ and @TRANSPORTSTART@ sections. The end result would look like this (plus any edits you may have already made):

@AUTH@

@BEGINACL@

@CONFIG@ system_filter_directory_transport = local_copy_outgoing
@DIRECTOREND@

@DIRECTORMIDDLE@

@DIRECTORSTART@

@ENDACL@

@RETRYEND@

@RETRYSTART@

@REWRITE@

@ROUTEREND@

@ROUTERSTART@

@TRANSPORTEND@

@TRANSPORTMIDDLE@

@TRANSPORTSTART@ local_copy_outgoing: driver = appendfile delivery_date_add envelope_to_add return_path_add group = cpaneleximfilter user = cpaneleximfilter mode = 0660 maildir_format = true create_directory = true

Now, make a copy of the existing system filter file to a custom location, so cPanel updates don’t mess with it:

cp /etc/cpanel_exim_system_filter /etc/cpanel_exim_system_filter_custom
Edit /etc/exim.conf.localopts and change the “systemfilter” option to match our new file:

systemfilter=/etc/cpanel_exim_system_filter_custom

Now, open _/etc/cpanel_exim_system_filtercustom and add the following block of code to the end of the file:

if $header_from: contains "@senderdomain.com" then unseen deliver "other@emailaddress" endif

Replace the blue text with the sender domain (or email address) and the email address that outgoing mail should be copied to.

Apply these new settings to the exim.conf and restart:

/scripts/buildeximconf

service exim restart
Now when you send email from the email address or domain specified in the filter file, it will be copied to the other email address.

source: http://www.thecpaneladmin.com/copy-outgoing-email-on-a-cpanel-server-with-exim/