If your account has a Root Domain Pointer (an additional domain that
points to your main site), you can activate an alias-based email
service for the pointer domain. What that means is any email address on
your primary domain will also accept messages sent to the same address
on the pointer domain.
For example, let's say your primary domain is primary.com, and you use pointer.com as a domain pointer. If you set up the email address
info@primary.com, that mailbox will also accept mail for
info@pointer.com.
The mail service for pointer domains is alias-only, so you cannot set
up a separate address on pointer.com. Any pointer.com addresses have to
point to an email address on the primary domain name.
sales@pointer.com
will not work unless sales@primary.com exists.
Note that if the same message is sent to info@primary.com and
info@pointer.com you will receive two copies of the message in the
info@primary.com mailbox.
For information on activating Domain Pointer Email Alias service see
this Knowledge Base article.