Shared mailbox management — create shared mailboxes and decide who can read, write, or administer each one.
Personal mailboxes are deliberately absent from this page. They're created automatically, there's exactly one per user, and nobody else is ever granted access to one — there is nothing here to manage.
Who can see this page
The page itself needs the "inbox" module permission. Individual mailboxes
are then filtered to those the viewer holds "admin" on (which their own
created mailboxes always are), so a "write" grantee on support@ can send
as it but can't hand access to someone else.