Returns configured delivery providers and the default instance. All secrets are redacted: SMTP passwords are blank; a configured googleDirectInjection has every attribute returned as "[REDACTED]"; and an M365 white-label provider carries an m365Config block with every attribute "[REDACTED]" (the block's presence signals the integration is configured — no value is exposed). Microsoft Teams notification-channel entries (serviceProvider "Microsoft Teams") are filtered out of DeliveryProviders, matching the console's email delivery views — Teams is a notification channel, not an email-delivery provider.