docs(campaign): define target-like mail evidence

docs/CAMPAIGN_DELIVERY_RUNBOOK.md

@@ -104,6 +104,19 @@ bed where possible:
 - IMAP append failure after SMTP acceptance.
 - Worker restart with queued, claimed, and sending jobs.
 
+For the maintained loopback baseline, run
+`dev/mail-testbed/run_campaign_acceptance.py`. It proves the public Campaign
+path for SMTP acceptance, IMAP append, repeat-send blocking, an SMTP connection
+failure before transmission, an explicit SMTP authentication rejection, and an
+IMAP authentication rejection after SMTP acceptance. Its evidence is an
+allowlisted classification/count projection; raw provider diagnostics and
+transport/account identifiers are deliberately excluded.
+
+The runner does not simulate a connection loss after SMTP DATA and does not
+restart a real worker. Keep those two checklist items open until a controlled
+fault proxy/target provider and supervised worker environment can produce the
+corresponding `outcome_unknown`, restart, retry, and reconciliation evidence.
+
 ## Reporting Checks
 
 - Partial delivery must show accepted, failed, and unknown counts separately.