When you setup a secondary domain in a VDS, it will not get it's own unique DNS zone file, but will instead be aliased to the primary domain, (causing the secondary domain to always work with the same mail server as the primary domain).

You can get around this by doing the following steps:

1. The DNS needs to be hosted externally - contact your registrar and have them point your domain name to another name server. Make sure it is NOT pointed to ns1.hardhathosting.net and NOT ns2.hardhathosting.net

2. DISABLE the mail server in your secondary domain's settings.

3. Modify the /etc/resolv.conf file to point to the new DNS server you have selected.  NOTE: You can use the IP addresses specified in the below example for the external name server unless you have another you prefer.

Example:  If the domain name is SomeDomain.dom, you would change the /etc/resolv.conf file to look like this

domain Somedomain.dom
nameserver 208.67.222.222
nameserver 208.67.220.220