As a TB user, I want clients to retrieve and authenticate to all personal and shared inboxes after sign in, so that I can access all of my assigned mailboxes without authenticating to each one separately.

Acceptance criteria:

* After the user successfully authenticates, fetch the personal and shared inboxes linked to their account.
* Authenticate the TB client to each returned inbox.
* Make successfully authenticated inboxes available in TB.
* Handle failures for an individual inbox without preventing access to other inboxes that authenticated successfully.