(default: false) If false, any attempt to destroy a Mailbox that still has Emails in it will
be rejected with a mailboxHasEmail SetError. If true, any Emails that were in the Mailbox
will be removed from it, and if in no other Mailboxes, they will be destroyed when the
Mailbox is destroyed.
(default: false) If false, any attempt to destroy a Mailbox that still has Emails in it will be rejected with a mailboxHasEmail SetError. If true, any Emails that were in the Mailbox will be removed from it, and if in no other Mailboxes, they will be destroyed when the Mailbox is destroyed.