Sender block — a server refused you as the sender (reputation, spam or policy). The only kind that is about your domain. Any one: open the row and read it. Two or more, or above 1%: hold sending.
Bounce rate — all bounces ÷ sent. Resend counts every bounce, whatever the cause, and may pause the account at 4%. Under 2% fine · 2–4% clean the list before the next queue · 4%+ stop sending. With few sends each bounce moves this a lot (1 bounce in 140 = 0.7%).
Complaints — any complaint: hold volume for a few days (send.js stop rule).
Dead address / dead domain — the mailbox or domain no longer exists. Stale data, add to unsubscribe.txt.
Internal-only group — info@ is a group that only accepts mail from inside the company. Unreachable from outside; add to unsubscribe.txt.
Already suppressed — Resend refused to send because this address bounced before.
Still retrying — delivery delayed; Resend keeps trying and it may still arrive.
Resend's own "Transient/Permanent" label is shown for reference only — it is often wrong about whether a bounce is permanent, so the cause is worked out from the server's text.