Login Issues in Cpanel Godaddy

Hi I have multiple cPanel's on GoDaddy in same server . and I'm maintaining different email accounts for different cPanel, but I'm facing a issue like i was able to login a different domain email from a another domains cPanel. For example let say my domain name is facebook.com and I was able to login twitter.com mail from Facebooks webmail login. webmail.facebook.com allows me to login in sample@twitter.com and it was able to see, get and send mail's as well. could any body guide me to set the configuration properly.