Mail mirroring question - mailboxes?

I have a question about how mail mirroring works. It says that all the emails on one domain will work on the other domain. But i’m not clear on how this works- what about mailboxes set up on the domain which is being mirrored- does the mirroring domain also have a mailbox created, or does it just work like an alias?

I would test this out but the domain I want to use “mail mirroring” on is currently pointing to a different, non-Dreamhost webhost. I want to set things up before I switch the nameservers to point to Dreamhost.

Mailboxes on domains using mail mirroring are shared between the two domains. If you have two addresses and, and is set to mail mirror, Alice and Bob’s mailboxes will also receive mail to and, respectively.

ok, thanks for the fast reply! I think that answers my question. So there will be duplicate mailboxes, if I understand correctly.

It doesn’t seem to work if I use forwards for and not regular mailboxes. The forwards of and then not mirrored by

Is that correct? And if so, is there another solution?