Disable Email For Single Account on WHM / Cpanel

If you are setting up MS Exchange for your domain hosted on a WHM / Cpanel server setup and migrating from a POP3 / IMAP account to an Exchange email account, soon you will realize that the emails sent by the local server is not being forwarded to the MS Exchange account but rather on the old POP3 / IMAP account. Similar to the situation of this administrator asking people from the Cpanel forums:

"Is there a way to disable email completely for an account? We are having a situation where one of our users hosts an in house exchange server. Theyre email works fine on their exchange server, but they can not send anyone email on their webserver and vice versa. It is getting stuck by looking for an email account on our server instead of on their actual mail server. The only way to resolve this that I can think of is to diable email all together for that account. Any suggestions? Thanks!"

Thankfully, the solution is very easy. Here are the steps:

1. Login to your ssh account as root.
2. Open up /etc/localdomains and remove their domain.
3. Open up /etc/remotedomains and add their domain.

After editing those files, the mails sent by the local mail server will now be sent to the MS Exchange account. 

Source: http://forums.cpanel.net/f5/disable-email-completely-single-account-61391.html