Sometimes you have an email account and you want to edit the email/hour for only one of the domain on the account, here is how to do that.

SSH to the server ssh domainHere.com
Edit the file /var/cpanel/users/userAccount file
Add or Edit a line like this
MAX_EMAIL_PER_HOUR-domainHere.com=100
Replace domainHere.com with the domain name in question, and 100 with the number of emails per hour you wish to allow.
Save the file and run /usr/local/cpanel/scripts/updateuserdomains