You can have multiple incoming adresses for a user.
However, as with all other Enterprise Email systems that I know (Exchange, Groupwise, etc.), every user can only have ONE outgoing internet address. this is used in corporate environments to ensure consistent appearance to the outside world.
in my personal case, my outgoing email address is always
first.last@scalix.com, i also have
first@scalix.com as an alias due to my long last name. still, i want all outgoing email to use the full name.
As for domains, the answer is simple. You don't have to do anything at all. Scalix does not accept email based on domains, but on directory-based address match, i.e. as soon as a user has an email address (including domain), scalix will accept messages for this user. This is working as designed and super helpful in coexistence scenarios as Scalix can easily be set to accept only the users that it knows about and forward all other traffic (even in the same domain) to the "old" mailserver.
Hope this helps,
Florian.