feat: pause campaign batches on SMTP failure

README.md

@@ -120,6 +120,11 @@ Platform RBAC and governance rules are documented in `govoplan-core/docs/`.
 - [Campaign handbook](docs/CAMPAIGN_HANDBOOK.md) provides the adaptive user, process, governance, technical, and operations perspectives.
 - [Campaign delivery runbook](docs/CAMPAIGN_DELIVERY_RUNBOOK.md) covers queueing, local vs Celery operation, retries, reconciliation, reports, and the live SMTP/IMAP test checklist.
 - Immediate delivery is bounded to 25 exact eligible recipient jobs by default. Deployments may set `GOVOPLAN_CAMPAIGN_SYNCHRONOUS_SEND_MAX_RECIPIENTS` (0–500), and tenants may narrow that ceiling through `campaign_delivery_policy.synchronous_send_max_recipients` in tenant settings.
+- Immediate Mail delivery preflights the selected SMTP transport before the
+  first effect and reuses a healthy bounded connection through Mail. Review and
+  send reports the batch state, connection/reconnect counts, and paused count.
+  A systemic authentication, sender, or connectivity failure pauses remaining
+  jobs; correct and test the Mail profile before explicitly resuming them.
 - Report-email preview uses the selected version's stored v5 Mail-profile evidence. Live report email fails closed until [govoplan-mail#17](https://git.add-ideas.de/GovOPlaN/govoplan-mail/issues/17) provides a durable, idempotent Mail-owned outbox and transport-attempt ledger; per-job CSV is off by default and requires `campaigns:recipient:export` when requested.
 - [Campaign/Mail profile boundary](docs/MAIL_PROFILE_BOUNDARY.md) defines profile-only delivery, runtime resolution, execution evidence, and the fail-closed legacy migration path.
 - [Recipient import guide](docs/RECIPIENT_IMPORT_GUIDE.md) covers user/admin workflows, mapping profiles, validation, and import evidence.