Symptoms#
- Messages landing in spam despite previously good placement
- Bounces mentioning policy, authentication, or reputation
- Provider dashboards showing a drop in reputation or authentication pass rate
Diagnosis steps#
- Confirm the configuration is live: query DNS from an external resolver and check the sending platform's settings page.
- Send to a seed mailbox and read the full headers, especially Authentication-Results.
- Compare the domains in From, Return-Path, and DKIM d= for alignment.
- Check provider dashboards (Google Postmaster Tools, Microsoft SNDS) for reputation and error rates.
- Review recent changes: new vendors, DNS edits, list imports, volume spikes.
Likely causes#
- Assuming 'encrypted' in Gmail means end to end; it usually means TLS in transit.
- Deploying S/MIME without a certificate lifecycle plan.
Fix and re-verify#
- Enforce TLS 1.2+ on inbound and outbound connections.
- Publish MTA-STS to prevent downgrade attacks.
- For regulated content, use S/MIME or a secure-message portal with recipient authentication.
- Log and report TLS failures via TLS-RPT.
Frequently asked questions#
Is Gmail encrypted?
Gmail uses TLS in transit and encryption at rest. End-to-end encryption requires S/MIME (Workspace Enterprise) or client-side encryption.