Error : A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:  test@domain.com   Unrouteable address”

Solution :

Suppose you have try to send emails from domain.com to any other email account and the server shows the above error then this problem is due the entry of your domain.com is present in /etc/localdomains file on remote server. You need to remove the domain.com entry from /etc/localdomains file and restart the exim service on the server.