Is it possible to setup domain1 so that it is simply an alias for domain2?

In other words:

- I have 3 domains:,, and that I want to be administered in unison rather than independently.
- I want to create as the primary/default domain, and and as pseudonyms for so that and are automatic "aliases" for It would also be nice if it is not even actually possible to directly create an account for and

(I'm not in command of all the jargon.. is this domain "aggregating", "masquerading", "forwarding"?)