Question about external accounts

[hispa]

Hello,

I have my zimbra configured at the moment with one domain (let's say foo.com), and some users have external accounts configured (they synchronized them) and can work well with them.

My questions are:

a) Once they have "migrated" their e-mails to Zimbra, can we add the domain from which they synchronized the emails as a local domain so we can begin to work with that domain and the mailboxes already migrated?

b) Right now in the administration console when i clic on "Accounts" it only shows me the accounts for the unique domain we have right now (let's say foo.com), how could i do so it show the external accounts also?