Getting 550-Unrouteable address errors

This happends when you move a site from a server where it was previously hosted to a new one and there's a website on the old server trying to e-mail you, in my case I had a forwarder setup.

To fix this kind of error:

This message was created automatically by mail delivery software.

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:

youremailhere@yourdot.com
SMTP error from remote mailer after RCPT TO::
host yoursite.com [22.33.44.235]: 550-Verification failed for
550-Unrouteable address
550 Sender verify failed

You can easily fix this removing the domain for which verification failed from /etc/localdomains.