Webhook Integration Checklist for SaaS Platforms

Decide which events you will consume, like inbound_received, parse_succeeded, parse_failed, and attachment_available, then map each to user-facing actions such as ticket creation or comment updates.

Include fields like event_id, tenant_id, occurred_at, headers, parts, and attachment metadata, and use a schema version field for backward compatibility.

Deduplicate by event_id and email Message-ID, storing a processing ledger so duplicate deliveries or retries do not create multiple objects.

Define per-attachment and total message size caps, virus-scan requirements, and move large attachments to object storage with signed URLs.

Use per-tenant secrets or endpoints and segregated queues so one customer's traffic or compromise cannot impact others.

Keep raw MIME for a short replay window and parsed artifacts for longer, aligning with customer contracts and deletion workflows.

Require TLS 1.2+ on the webhook endpoint, disable weak ciphers, and enable HSTS to prevent downgrade attacks.

Validate a signature header using HMAC-SHA256 and reject requests with stale timestamps to mitigate replay attacks.

Use a kid header and support overlapping secrets during rotation, removing old keys after verification drops to zero.

Restrict access to known sending IPs and use rate limiting or bot protections tuned for machine-to-machine traffic.

Write to your datastore or queue before acknowledging, respond 5xx for transient errors to trigger retries, and ensure handlers are idempotent.

Set max body size and use streaming or chunked processing so large messages do not exhaust memory; reply 413 with guidance when exceeded.

Encrypt stored emails and attachments and redact tokens, secrets, and PII in structured logs to minimize leakage.

Expose a single POST endpoint like /webhooks/email-inbound separate from app routes and block unsupported methods.

Parse and verify the signature, enqueue a task, and return 202 or 200 within 100-300 ms, attaching a correlation_id for tracing.

Store the original message and a normalized JSON representation with content hashes so you can replay parsing logic later.

Handle multipart/alternative, related, and mixed parts, decode quoted-printable and base64, and resolve Content-ID inline images.

Convert encodings to UTF-8, apply Unicode normalization, and scrub HTML to prevent XSS in admin and customer-facing views.

Use Message-ID, In-Reply-To, and References to map messages to conversations or tickets and fall back to subject heuristics only when necessary.

Classify DSN reports and Auto-Submitted headers to suppress loops, update suppression lists, and annotate events for analytics.

Expose your local endpoint with ngrok or cloudflared, capture real webhook payloads, and build a fixture library from multiple email providers.

Include fixtures with wrong secrets, modified bodies, and expired timestamps and ensure the endpoint returns 401 or 403 consistently.

Upload payloads near size limits to validate streaming, backpressure, and correct 413 responses with actionable error bodies.

Send malformed boundaries, nested multiparts, and non-UTF-8 charsets to confirm your parser degrades gracefully without crashes.

Replay the same event_id concurrently and out of sequence to validate idempotent handlers and consistent final state.

Run contract tests for v1 and v2 payloads, ignoring unknown fields by default and guarding breaking changes behind feature flags.

Measure time-to-ack, time-to-parse, parse success rate, queue depth, and retry counts per tenant and export to Prometheus or OpenTelemetry.

Page on spikes in signature failures, 5xx response rates, DLQ growth, and abnormal latency so incidents are caught early.

Emit JSON logs including correlation_id, event_id, tenant_id, and message hashes while redacting sensitive content by default.

Build an internal console to inspect failed deliveries, edit configs, and replay events once a fix is deployed.

Document error signatures like invalid signature or MIME parse failures and provide Grafana dashboards with drill-down to sample payloads.

Record who accessed email content and when and support tenant exports and deletions to satisfy compliance and enterprise requirements.