aws-messaging-webhook

One Rust Lambda function that receives AWS messaging events from Amazon SNS, records them in DynamoDB, and republishes them to an EventBridge bus your applications subscribe to. It handles:

• AWS End User Messaging (EUM): inbound SMS and delivery receipts.
• Amazon SES: sending events (bounces, complaints, opens, clicks) and inbound mail.

Optionally, it also runs a mailbox on SES with an HTTP API to read and send mail.

How it works

EUM / SES ─► SNS ─► Function URL (HTTPS) or direct invoke
                      │
                      ├─ verify   SNS signature + topic allowlist
                      ├─ persist  DynamoDB, one conditional write per event
                      ├─ act      opt-outs, suppression, delivery feedback
                      │
                      └─ DynamoDB stream ─► relay ─► EventBridge ─► your apps

• Verify. Every message must carry a valid SNS signature and come from an allowlisted topic.
• Persist. A conditional write makes SNS redeliveries harmless.
• Act. STOP/START update the EUM opt-out list. Hard bounces and complaints go on the SES suppression list. Delivery receipts send message feedback.
• Publish. A stream relay publishes each saved event, with retries and a dead-letter queue.

Subscriptions confirm themselves. If someone abuses an UnsubscribeURL, the function re-subscribes.

Quick start

Install Rust, cargo-lambda and the AWS SAM CLI, then:

sam build
sam deploy --guided   # set pAllowedTopics to your account id

Subscribe your SNS topics to the endpoints the stack outputs. See docs/deploy.md.

Important

Set pAllowedTopics. A valid signature proves only that a message came from SNS in some account. Keep raw message delivery off on every subscription.

Mailbox

Set pMailDomain and pMailInbox to receive mail at <inbox>@<domain>. Inbound mail is stored in S3 and DynamoDB, threaded, and exposed through a /v0 API that also sends mail.

• Setup: parameters and five one-time steps after the first deploy
• API: routes, labels, filtering and sending
• Events: message.* events and webhook delivery
• Tracking: opens, clicks and custom tracking domains
• Storage: mail table, bucket layout and retention
• Runbook: stuck sends and failed ingests

Documentation

Doc	Covers
Deploy	Parameters, topic subscriptions, retry behavior
Events	EventBridge detail types and payloads
Data model	Events table and cross-account read access
Operations	Logs, metrics, alarms and an end-to-end check
Mailbox design	Why the mailbox is built the way it is

Development

cargo test --workspace   # no AWS account needed
cargo clippy --all-targets --all-features -- -D warnings
prek run                 # fmt, clippy, deny, actionlint, zizmor

Crate	Purpose
crates/mailbox	Pure mailbox domain: message/thread/send types, ids, labels, MIME parsing and building, wire shapes
crates/mailbox-store	The mail table: keys, transaction planner, the Table seam and the Mailbox over it
crates/sns-message-verifier	SNS signature verification. The test-fixtures feature signs test messages
crates/webhook	The Lambda function (package aws-messaging-webhook)
crates/webhook-test-support	Fakes and request harness shared by the webhook crate's integration tests

Dependency direction: aws-messaging-webhook -> mailbox-store -> mailbox.

Debug builds read SNS_CERT_HOST_OVERRIDE to run against a local fake SNS under cargo lambda watch. Release builds always verify.

License

Licensed under either of the Apache License 2.0 or the MIT license, at your option.