failed
perm_failed
sent
suppressed
unsubscribed
=== label sets ===
4:  queued -> processing -> sent (Gmail accepted, message ID recorded)
278:            outcome="submitted",
305:        # ------------------------------------------------------------- accepted
307:        attempt.outcome = "accepted"
326:                          message_id=msg_id, detail=f"accepted via {client.method}"))
384:    cr.status = "queued"
438:        _push_dlq(campaign.id, cr.id, error)
453:def _push_dlq(campaign_id, cr_id, error):
457:        rdb.rpush("dlq:send", f"{campaign_id}:{cr_id}:{error[:200]}")