The alert e-mail addressed ALL recipients in a single To:. When the admin
fallback list contains an undeliverable address (e.g. a seeded admin on a
non-routable domain), a receiving provider like Gmail sees the mixed
To: including a nonexistent recipient, scores the message as spam, and
silently drops it — for the valid recipients too (not even the spam
folder). A single-recipient test mail from the same relay arrived fine,
which is what isolated it: the shared To: was the difference, not SMTP.
Send one message per recipient instead (best-effort, per-address error
logging). A bad address now only fails its own send, and no recipient's
address leaks to the others. Diagnosis confirmed the worker sends over
real SMTP (mail.default=smtp, host=mail.thinkidoo.com) — this was purely
the recipient-list shape hurting deliverability.
Tests updated: two configured recipients now queue two messages, each
with a single To.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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