docs: document the Campaign-to-Mail delivery boundary

docs/CAMPAIGN_DELIVERY_RUNBOOK.md

@@ -15,6 +15,8 @@ been validated, built, reviewed, and locked.
 ## Before First Live Use
 
 - Use dedicated non-production SMTP/IMAP credentials.
+- Store and test those credentials in a Mail-module profile. Campaign must
+  contain only the selected `server.mail_profile_id` reference.
 - Start the repository test bed in `dev/mail-testbed/` when a local
   production-like SMTP/IMAP server is sufficient.
 - Use a dedicated mailbox/folder for append-to-Sent tests.
@@ -64,6 +66,13 @@ Before the first live send for a sender domain or mail-server profile:
 - `claimed` or `sending` that does not progress: treat as a worker interruption.
   Re-run worker handling or reconcile if SMTP may already have accepted the
   message.
+- IMAP `appending`: A worker owns the durable append claim. Do not start a
+  second append; if the worker cannot finish, reconcile only after checking the
+  mailbox.
+- IMAP `outcome_unknown`: Never append automatically. An operator with
+  `campaigns:campaign:reconcile` must record an evidence note and resolve it as
+  `imap_appended` or `imap_not_appended`. Only the latter becomes explicitly
+  retryable.
 
 ## Reconciliation