A domain pointer points the entire domain. So all the emails from one domain are set up on the other domain.
The specific method is a symbolic link in /etc/virtual/ from the pointer domain to the pointee domain.
And that's where all the email information is stored.
Both domains share the same mailbox, so when picking up email the user only logs into the mailbox at the original domain.
If this doesn't work for you then you should delete the pointer, set up the domains separately, and create separate mailboxes. You can use an .htaccess file to set up a redirect.
Jeff