Email Authentication Checklist for Financial Services

List every system sending invoices, statements, payment notifications, and auditor mail. Tie each sender domain to a mailbox or inbound API endpoint so authentication can be enforced consistently.

Set a policy that requires SPF pass, DKIM pass, and DMARC pass with strict alignment for high-risk streams like payments and payroll. Document escalation from monitor to quarantine to reject per stream.

Link GLBA, SOX, PCI DSS, and ISO 27001 obligations to concrete email authentication controls and audit logging. Ensure policies cover PII and cardholder data handled via email attachments and inline content.

Name accountable owners for each sending and receiving domain, with CAB-reviewed change windows for SPF, DKIM, and DMARC updates. Require rollback plans to avoid mail flow disruptions during DNS changes.

Tag mailboxes and routes that carry invoices, payroll files, or bank statements as high sensitivity. Apply stricter DMARC alignment and auto-reject rules for these streams in the parsing and delivery pipeline.

Include clauses that vendors must publish valid SPF and DKIM and align DMARC to the exact sending domain. Define SLAs for fixing authentication breaks that impact invoice processing or reconciliation.

Create TXT SPF records that list only approved MTAs and use include for major providers. Keep total DNS lookups at or below 10 and avoid ptr to prevent spoofing and latency in financial email receipt.

Generate 2048-bit DKIM keys per domain or subdomain, publish selectors in DNS, and rotate keys on a 90-day schedule. Validate signatures on receipt and log the selector and body hash for audits.

Publish a DMARC record with adkim=s and aspf=s, start with p=none and increase to quarantine then reject with pct sampling. Send rua and ruf reports to monitored mailboxes and aggregate to dashboards.

Sign zones for sending and receiving domains with DNSSEC to reduce record tampering risk. Coordinate with your registrar and monitor for DS record propagation before tightening authentication enforcement.

Publish MTA-STS policy to require TLS for SMTP and set TLS-RPT to receive transport failure reports. Alert when vendors downgrade or fail TLS so finance emails do not traverse in plaintext.

Use dedicated subdomains (e.g., invoices.example.com) with strict DMARC and locked MX routes to your inbound API. This avoids cross-domain misalignment and simplifies per-stream enforcement.

On message receipt, extract Authentication-Results and expose SPF, DKIM, and DMARC verdicts, alignment flags, and reasons in webhook or REST payloads. Make these fields mandatory for downstream processors.

Gate parsing and attachment extraction on a DMARC pass for high-risk streams. Quarantine messages failing DMARC and require human review before any ERP or treasury system intake.

For payroll and statements, require strict From-domain alignment with the DKIM d= and SPF domain. For lower-risk notifications, allow relaxed alignment but record the mode in audit metadata.

Only accept PDF, CSV, or XML attachments from authenticated, allowlisted domains. Block executable or macro-enabled documents unless explicitly approved, and log the decision with authentication context.

Store the canonicalized header set and DKIM bh= values in immutable logs. This aids forensic analysis and proves that the content parsed into JSON matched the signed payload from the sender.

When deduplicating threads or invoices by Message-ID, include SPF/DKIM/DMARC outcomes in the dedup key. Prevent unauthenticated duplicates from overwriting authenticated messages in invoice pipelines.

Enforce STARTTLS with modern ciphers and reject plaintext sessions for financial mailboxes. Log TLS version and cipher to your webhook payload so consumers can verify transport security alongside authentication.

Route DMARC fail or alignment-fail messages to a moderated queue with redacted previews. Provide quick actions to request vendor remediation, approve temporary exception, or reject with bounce.

For messages forwarded by ticketing systems or accounting inbox rules, verify ARC chains to preserve authentication. Accept only valid ARC seals and flag anomalies for manual review.

Cross-check From domains against a watchlist of lookalikes of your major vendors and banks. Combine this with DMARC verdicts to block high-risk spoofs and raise incidents with fraud teams.

Store private keys in hardware security modules and automate rotation with audit approvals. Update selectors in DNS during maintenance windows and validate signatures immediately after each change.

If business requires temporary acceptance of a vendor failing DMARC, issue a time-limited exception tied to a mailbox and domain. Record justification, approver, and all authentication data for later review.

Create non-production domains mirroring SPF, DKIM, and DMARC policies to test changes safely. Send sample invoices and statements through the inbound API to validate parsing and verdict fields.

Coordinate with each vendor to send test emails that pass, fail, and softfail SPF/DKIM/DMARC. Confirm webhook payloads reflect correct verdicts and that enforcement gates behave as designed.

Test nested multiparts, TNEF, base64 anomalies, and unusual charsets. Ensure the parser maintains authentication context and does not mis-associate attachments or inline content with unauthenticated senders.

Simulate transient failures and verify retry logic includes consistent authentication fields. Use idempotency keys that combine message identifiers with authentication results to avoid duplicate processing.

Reconcile external rua aggregates with your measured pass rates per vendor. Investigate discrepancies that could indicate DNS drift, forwarding paths, or parser mistakes in Authentication-Results extraction.

Practice reverting SPF changes that accidentally exceed lookup limits or remove valid senders. Validate that inbound email APIs and mailboxes recover without losing authentication checks.

Track pass rates per vendor and per mailbox, with thresholds for immediate alerts when critical streams degrade. Tie alerts to recent DNS changes or key rotations for rapid diagnosis.

When a vendor's authentication fails beyond agreed SLA, send templated alerts with evidence and remediation steps. Escalate to account managers if finance processing is blocked.

Continuously scan SPF records for risky macros and count total lookups. Alert if limits are breached or if includes pull in unexpected networks that could weaken trust.

Collect TLS-RPT and internal metrics to spot sessions negotiating weak ciphers or failing STARTTLS. Block downgraded sessions for sensitive streams and coordinate fixes with vendors.

Store message metadata, Authentication-Results, DKIM selectors, and parsing outcomes in append-only storage. Provide auditors with search across invoices and statements linked to authentication decisions.

On suspected spoofing, freeze intake, preserve evidence, notify fraud teams, and start takedown of lookalike domains. Use aggregate DMARC reports and webhook logs to scope and contain the attack.