PrivilegedMailboxRequirement

enum PrivilegedMailboxRequirement

What a user must hold to read a privileged mailbox–and, equivalently, who the mailbox’s phantom account fans out to when it’s addressed or participates in a chat. Expressing this as data (rather than writing “is this user a moderator or does this user have role X” by hand at each call site) means the roster expansion and the access check can never drift apart.