This is possible. Each user account will work with each domain you host. You do not need to do anything further than setup up each of the virtual domains.
I know this works, as I have eight domain names hosted on my e-smith server, and my user account can receive email sent to any of the domains.
For example you can reply to me at:
james@shields.net.au
james@geelongcats.com
james@scottiesvic.asn.au
etc, etc, etc.......