Trying to restore a mail file from a recovery database

I am trying to recover an exchange mail file from a recovery database, I tried to browse the database but got no results

[PS] C:\>Get-MailboxDatabase rdb

Name                           Server          Recovery        ReplicationType
RDB                            CBSEXC001       True            None

[PS] C:\>Get-MailboxDatabase rdb | get-mailbox
[PS] C:\>

if I can't browse the mailboxdatabase, how do I know the users mailbox is there?

any information would be appreciated