How it fits together

Four moving parts. Knowing which one is at fault is most of debugging a mail problem, so it is worth five minutes.

The pieces

Piece	What it does	Where it runs
The app	The web UI, the API, the database	Your server, in Docker
Amazon SES	Hands your outbound mail to the internet	AWS
The inbound worker	Catches mail for your domains, posts it to the app	Cloudflare
R2	Holds attachments and raw messages	Cloudflare

Postgres holds everything else, and is the only thing you have to back up besides the R2 bucket.

Sending

your code ──▶ POST /api/v1/emails ──▶ the app ──▶ SES ──▶ the internet
                                         │
                                         └──▶ Postgres (the message, its thread)

SES then reports what happened to the message — delivered, bounced, complained, opened — through an SNS topic that posts back to the app. That is what fills in a message's status, and what fires the email.*webhooks.

Delivery reporting only works when a message was sent with a configuration set attached. Setting SES_CONFIGURATION_SET is what attaches it.

Receiving

the internet ──▶ Cloudflare Email Routing ──▶ the inbound worker
                                                    │
                                                    ▼
                                    POST /api/inbound (signed) ──▶ the app
                                                                     │
                                                          ┌──────────┴────────┐
                                                          ▼                   ▼
                                                      Postgres            R2 (raw, files)

The worker is deployed from the app, under Settings → Inbound worker. You paste a Cloudflare API token once; there is no wrangler step of your own.

Every call from the worker is signed with INBOUND_WEBHOOK_SECRET, so nothing else can post mail into your instance.

Live updates

The app uses Postgres LISTEN/NOTIFY with server-sent events, so a message that arrives appears in an open browser without a refresh. Nothing polls.

Where mail is threaded

An arriving message joins an existing thread if its In-Reply-To or References matches one already stored. Failing that, an identical subject in the same mailbox within thirty days joins it too. Otherwise it starts a new thread.