To disable the local mail delivery for single domain name refer to the following steps but make sure that you are logged in as a root user. If any domain using the external mail server like google MX record etc then only disable the local delivery for mails.
Login in to the shell and open the file /etc/localdomains
nano /etc/localdomains
Search the domain name for which you want to disable the local delivery and comment the line or remove the domain from the file and save the file
Now open the file /etc/remotedomains
nano /etc/remotedomains
Add the domain name which we have removed the from the localdomains file.
