A week ago one of our clients account been compromised and the attacker used the server to blast emails. as a system administrator my task was to prevent any outgoing email from the account before I start to investigate the attack and remove any kind of scripts from the hosting account. Studying cPanel files made me to come around following solution.

To disable email for one account we can change the permission of /etc directory for that particular user, using our root power.
simply use following commands:

chmod 0 /home/username/etc
 chattr +ia /home/username/etc

You need to replace username with your user username. Once this is done the user will not be able to send anymore emails from local server. To undo this you should run the chattr once more:

chattr -ia /home/username/etc 
chmod 750 /home/username/etc
That’s it, Stay safe… out of spam!