To prevent outbound spamming from cPanel, you can setup/Configure maximum email that can be send outside. You can set these in /var/cpanel/users/username file with the following options:
MAX_EMAIL_PER_HOUR=#
MAX_EMAIL_PER_HOUR-domain.com=#
First option is for the entire domain and the second option is for the domain/ subdomain.
Once this is specified, you need to execute the below command for this to get updated,
=-=-
/scripts/updateuserdomains
/scripts/update_email_limits
=-=-=
You can configure this globally for the server from WHM from the following location
-=-=
WHM > Tweak Settings > Max hourly emails area.
-==-
Done
MAX_EMAIL_PER_HOUR=#
MAX_EMAIL_PER_HOUR-domain.com=#
First option is for the entire domain and the second option is for the domain/ subdomain.
Once this is specified, you need to execute the below command for this to get updated,
=-=-
/scripts/updateuserdomains
/scripts/update_email_limits
=-=-=
You can configure this globally for the server from WHM from the following location
-=-=
WHM > Tweak Settings > Max hourly emails area.
-==-
Done