Using NW6 DNS & GWise 6.5..

I currently get email at my primary domain, ie. email@ctw.com. For
testing
purposes I would also like to be able to get email at
email@us.ctw.com, so
that my email tests don't interfere with my production email. I will
also
be bringing up a secondary email system to handle email@us.ctw.com.

Can anyone tell me how to configure my DNS so that I can receive email

like this? I'm assuming I need to create a secondary domain under
ctw.com,
but I'm not sure how to accomplish this nor what records I will need
to
create.

TIA,

phil