All packsTransactional Email Deliverability CoreSolve
email deferred send never retried dropped silently
A deferred send with nothing replaying it is a dropped send
Warmup correctly defers a send that would exceed the daily cap -- but a deferral with no drain routine to replay it later is functionally a silent drop.
What goes wrong
Deferring a send that would exceed the day's warmup cap is the right call -- but deferring only helps if something eventually retries it. A system that records a deferred row and stops there has, in practice, dropped that email: the password-reset or receipt the user was waiting on never arrives, and nothing in the deferral itself schedules a follow-up attempt.
Why agents get it wrong
Implementing the deferral check ("if over cap, don't send, record it") reads as a complete feature on its own, and it passes any test that only checks "a send over the cap doesn't go out." Building the replay routine is a second, separate piece of work that isn't implied by the deferral logic itself -- it's easy to ship the half that prevents over-sending and never build the half that un-defers anything.
What Transactional Email Deliverability Core pre-decides
The pack ships drainDeferred() as a first-class routine, not an afterthought: it replays deferred rows in FIFO order (oldest first, so a busy day's early senders don't starve behind later ones), stays budget-bounded against the same day's remaining warmup allowance, and marks each replayed row with replayed_at so a second drain run -- cron overlap, manual retry -- can't double-send. GO-LIVE-CHECKLIST.md has the buyer schedule it on day one, specifically so nothing sits deferred waiting on a script that was never scheduled.
Source: ARCHITECTURE.md 'Deferred-send drain'