Send emails from Rust
Transactional and marketing email from async Rust services. One reqwest call, and a message ID you can follow to the inbox.
✓Free to start. Unlimited contacts on every tier.
One request, complete trace
Request
POST /api/v1/emails
Authorization: Bearer aem_…
Idempotency-Key: welcome-8f21
{ "to": "[email protected]", "template": "welcome" }
202 Accepted
{ "id": "msg_7ca31", "status": "queued" }
[ 01 / 04 ]Quickstart
How do I send email from Rust?
Three steps from no account to a queued email. No crate of ours needed.
Create an API key
In the dashboard, open Settings → API & MCP and create a key with the Send + manage permission (the default). It starts with aem_ and is shown once.
Store it as an environment variable
Keep the key on your server. Your code reads it with std::env::var("AEM_KEY").
Terminalexport AEM_KEY="aem_..."Send the email
POST the recipient and a published template with reqwest (json feature on). error_for_status() turns a 4xx or 5xx into an error, and a retry with the same Idempotency-Key won't send a second email.
send_welcome.rslet client = reqwest::Client::new(); // build once and reuse it let response = client .post("https://sendandretain.com/api/v1/emails") .bearer_auth(std::env::var("AEM_KEY")?) .header("Idempotency-Key", format!("welcome-{}", user.id)) .json(&serde_json::json!({ "to": user.email, "template": "welcome" })) .send() .await? .error_for_status()?;Keep the message ID
A 202 means queued, not delivered. Store the id; delivery, bounce, and complaint events arrive later on your signed webhook.
202 Accepted{ "id": "msg_7ca31", "status": "queued" }
[ 02 / 04 ]In production
What does a production Rust integration need?
One reused async client
Build the reqwest client once with a timeout, and model the request and response with your own serde types.
Retries with the same key
Keep transport errors, API errors, and accepted sends distinct. Retry only the temporary ones, with the same Idempotency-Key.
Webhooks checked on the raw body
Take the body as Bytes before deserialising, so the signature covers the exact bytes.
Events for marketing email
Send product events like signup or trial started. Automations you've turned on decide which email goes out.
[ 03 / 04 ]Example prompts
What can you ask your coding agent to do in Rust?
Paste these into Claude Code, Cursor, or Codex. Connect the MCP server and it can build the templates and automations too.
Email client
“Write a Send & Retain email client with reqwest and serde, one shared client, and an error enum that separates transport, API, and accepted results.”
Retries
“Add retries with backoff to our email sends. Reuse the same Idempotency-Key and never retry 4xx responses.”
Webhooks
“Add an axum handler that verifies Send & Retain webhook signatures on the raw Bytes body and flags bounced addresses in our database.”
Trial automation
“Send a trial_started event to Send & Retain when a trial begins, then build a paused trial automation for it.”
[ 04 / 04 ]Related
More ways to send email from Rust
Questions people ask us
Send your first email from Rust.
Create a key, make one call, and follow the message ID to the inbox.