You can use the EXIM queue interface to send commands to your WHM/cPanel to take immediate actions if you see an outgoing SPAM activity for your local email (as shown in the example images below) .
stop username
It stops outgoing email for the user username
unstop username
It allows outgoing email for the user username
suspend username
It suspends the account for the user username (reason "outgoing SPAM")
unsuspend username
It unsuspends the account for the user username
change email@domain.com
It changes current password of the account email@domain.com with a random password .