[eaigner]

Not sure if I completely understood your requirements, but you can add several custom domains (number depends on the plan) to your account, create mailboxes and aliases for them and can send and receive from those addresses as well.

Those are added to your account and can be accessed as individual mailboxes or via the unified inbox. They are not separate accounts with separate logins. Enterprise grade account management would be a feature to add at some point in the future.