you can create up to 5 mailboxes through the customer portal. (each mailbox has its own unique login ID and password)
For example you would create a mailbox for each member of your family, so they have their own account with their own password.
For each mailbox, you can assign up to five aliases (identities) associated with it.
so for example for a given mail box you could assign 2 aliases a home one and a work one.