Inbound Email Processing Checklist for Financial Services

Identify which parts of inbound emails (headers, body, attachments, signatures) qualify as business records under SEC 17a-4, GLBA, SOX, PCI DSS, and GDPR. Document how each artifact flows through your intake, parsing, storage, and archival path.

Set record-retention periods by document type (invoices, statements, trade confirmations), and implement WORM storage with verifiable immutability. Ensure legal hold can freeze related emails and parsed JSON without breaking downstream processing.

Pin storage and encryption key locations to required jurisdictions for banking clients, with customer-specific tenancy where needed. Prove that raw MIME, parsed JSON, and audit logs never leave approved regions.

Tag PAN, SSN, account numbers, and IBAN as sensitive, and mask values in event logs and dashboards (for example last 4 only). Only keep fields necessary for AP automation or reconciliation, and purge unnecessary email content.

For any inbound email API provider, capture controls for encryption, access, incident response, and subprocessor oversight. Align responsibilities for TLS enforcement, key management, malware scanning, and retention.

Maintain a controlled list of approved billing and bank addresses, and require DMARC alignment for these senders. Route non-aligned or unknown sources to quarantine for manual review.

Use a separate subdomain (for example mail.yourbank.example) for inbound processing with MTA-STS and TLSRPT configured. Ensure MX targets are highly available and enforce STARTTLS with TLS 1.2+.

Validate SPF and DKIM and enforce DMARC p=reject for known billing and bank domains. Record pass/fail results in the parsed event payload for downstream fraud analytics.

Use addresses like invoices+client123@subdomain.example to segment clients or entities. Map the plus tag to tenant IDs and apply strict isolation rules before processing MIME content.

Route based on sender domain, mailbox, and subject patterns (for example regex on 'Invoice', 'Statement', 'SWIFT MT940'). Assign each route to a parsing pipeline tuned for the expected document type.

Deploy multi-region MX with automatic failover and durable SMTP queues to survive provider or DC outages. Validate recovery times with failover drills and synthetic inbound traffic.

Allow PDFs, CSVs, OFX/QFX, CAMT, and ZIP with nested PDFs, and cap sizes per type (for example PDFs up to 20 MB). Reject or quarantine risky formats like macro-enabled Office files.

Require TLS 1.2+ with modern ciphers and prefer TLS 1.3, with MTA-STS to prevent downgrade attacks. Log negotiated protocols and cipher suites for every inbound session.

Verify digital signatures from trading counterparties and vendors, and include signer identity, certificate chain, and timestamp in the JSON payload. Reject or quarantine messages with invalid signatures.

Store private keys in an HSM or cloud KMS with role-based access and audit logs. Automate envelope decryption in the intake path without exposing plaintext in transient logs.

Inspect PDFs, ZIPs, and Office files for malware and detonate suspicious files in a sandbox. Only pass clean artifacts to the parser and tag events with scan verdicts and hashes.

Score inbound messages for homoglyph and lookalike domains of approved banks and vendors. Route high-risk messages to a quarantine mailbox and require manual approval before webhook delivery.

Use short-lived credentials, automatic rotation, and secret scoping for webhook HMAC, mTLS certs, and S/MIME keys. Revoke and roll keys on schedule and after any incident.

Handle RFC 2045-2049 and 5322 edge cases including nested multipart/mixed, multipart/related, and malformed boundaries. Prefer text/plain when available, and sanitize HTML before extraction.

Decode base64 and quoted-printable accurately, resolve CID-linked images, and capture key headers like Message-ID and Received. Store a content hash of the raw MIME for audit and deduplication.

Standardize fields like vendor_name, invoice_number, currency (ISO 4217), net_total, tax_total, account_id, and value_date with ISO 8601 timestamps. Validate schema before webhook delivery to reduce downstream errors.

Parse PDFs with templates or ML, and natively ingest CSV, OFX/QFX, CAMT.053, and MT940. Cross-check totals, balances, and control sums to prevent posting corrupted data.

Mask PANs and account numbers in payloads and logs, and store a salted hash or token for matching. Keep full values only in a secure vault when absolutely necessary and record access in audit logs.

Use Message-ID plus a content digest to detect duplicates and suppress reprocessing on retries. Track In-Reply-To and References to link document revisions or conversations tied to the same invoice.

Require client-authenticated TLS and verify an HMAC header with a rotating secret for each request. Reject stale timestamps and mismatched signatures to prevent replay.

Build idempotency using Message-ID plus a canonical payload hash, and store a processing ledger. Ensure posting to ERP/AP or core banking is exactly-once even under retries.

Retry failed webhooks with backoff and jitter, then move to a dead-letter queue after a cap. Provide a replay API to reprocess messages after downstream maintenance or fixes.

Enable cursor-based polling with time or ID checkpoints when webhooks are paused. Rate-limit aggressively and audit who enabled polling and why.

Wrap writes to AP/GL systems and compliance archive in a transactional outbox or saga pattern. Emit confirmation events only after both systems acknowledge receipt.

Curate signed and unsigned samples for invoices, ACH/NACHA notices, CAMT statements, FX trade confirms, and remittance advices. Include edge cases like multi-currency, credit notes, and partial payments.

Set target accuracy (for example 99%+ for totals and 99.5% for currency and date fields) and fail builds when thresholds drop. Track precision/recall by field and vendor template.

Fuzz MIME boundaries, send malformed headers, and simulate phishing with lookalike domains. Test large PDFs and ZIPs to validate timeouts, memory limits, and quarantine behavior.

Alert on SMTP accept rate, parse success rate, webhook latency, retry counts, and DLQ depth. Create dashboards segmented by sender, document type, and tenant to surface anomalies quickly.

Record receipt time, TLS parameters, authentication results, parsing decisions, and outbound delivery status with SHA-256 hashes in a chain. Store logs in WORM for 7+ years with periodic integrity checks.