List mailboxes visible to the current account

curl -X GET "https://example.com/v1/mailboxes"

{
  "mailboxes": [
    {
      "mailboxId": "f16f762c-c61b-441d-8b9c-9aff4650cbe1",
      "accountId": "3d07c219-0a88-45be-9cfc-91e9d095a1e9",
      "address": "user@example.com"
    }
  ],
  "nextCursor": "53a4a333-2825-45a4-80d2-5f430d088f36"
}