Supabase

Send email from a Supabase Edge Function

Supabase does not send app email for you beyond its own auth messages, so transactional mail from a Supabase project goes through an Edge Function. The function below takes a recipient, subject and body, adds an idempotency key, and sends it with one request to Warmerly's REST API from the Deno runtime.

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Before you write any code

Four steps, the same in every framework. Warmerly is REST only today: no SMTP relay, webhooks, templates or attachments yet.

Step 1: Add and verify a sending domain
In Warmerly open Transactional email, add the domain you send from (for example mail.example.com), publish the DNS records it shows at your DNS provider, then verify. Use a domain or subdomain you do not use for cold outreach.
Step 2: Create a Sending API key
Under Transactional email, API keys, create a key with the Sending permission, optionally limited to that domain. It starts with wm_tx_ and is shown once, so copy it straight into your secrets store.
Step 3: Store the key as WARMERLY_TX_KEY
Set it as a function secret with the Supabase CLI: supabase secrets set WARMERLY_TX_KEY=wm_tx_xxxx. Then deploy with supabase functions deploy send-email.
Step 4: Add the code below and send a test
A successful request answers 202 with the email's id and a status of sent (or queued, which Warmerly retries for up to 24 hours). The free plan is 5,000 emails a month with no card.

The code

Copy these into your project. The request is the same one the API reference documents; nothing is hidden behind a package.

supabase/functions/send-email/index.ts

// supabase/functions/send-email/index.ts
const ENDPOINT = "https://app.warmerly.com/api/v1/transactional/emails";

type Payload = { to: string; subject: string; html?: string; text?: string; requestId: string };

Deno.serve(async (req: Request) => {
  if (req.method !== "POST") return new Response("Method not allowed", { status: 405 });

  const { to, subject, html, text, requestId } = (await req.json()) as Payload;

  const res = await fetch(ENDPOINT, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${Deno.env.get("WARMERLY_TX_KEY")}`,
      "Content-Type": "application/json",
      // Reuse the same requestId when you retry the same message and it is sent once.
      "Idempotency-Key": requestId,
    },
    body: JSON.stringify({ from: "Acme <noreply@mail.example.com>", to, subject, html, text }),
  });

  const body = await res.json().catch(() => ({}));
  return new Response(JSON.stringify(body), {
    status: res.status === 202 ? 200 : 502,
    headers: { "Content-Type": "application/json" },
  });
});

Using it

Your app, or a Database Webhook

// From your app (supabase-js), or call it from a Database Webhook on insert.
const { data, error } = await supabase.functions.invoke("send-email", {
  body: {
    to: "jane@example.org",
    subject: "Welcome",
    text: "Thanks for signing up.",
    requestId: `welcome-${user.id}`,
  },
});

What to know about Supabase

Protect the function: Edge Functions require a valid JWT by default. Keep that on, and add your own checks about who may email whom, so the function cannot be used to send arbitrary mail.
Send on insert: To email when a row is inserted, add a Database Webhook that calls the function, and put the recipient and a stable id in the payload.
Supabase's own auth emails: Sign-up confirmation and password-reset messages come from Supabase Auth, which sends over SMTP. Warmerly has no SMTP relay yet, so this function is for the emails your own code triggers.

When the API does not send

Every refusal has a code in the response body, at error.code. These are the ones to handle, and whether to retry.

Error codes the send endpoint can return, what they mean and whether to retry
Status	Code	Meaning	Retry?
400	bad_request	Invalid body, or the From address is not on a verified sending domain.	No: fix the request
403	forbidden	The key is limited to a different sending domain.	No
403	sending_paused	Sending is paused for the workspace (bounce or complaint rate, or under review).	No: contact support
422	content_rejected	The message was refused by abuse screening.	No, not unchanged
429	rate_limited	The hourly or daily sending limit was reached.	Later
429	quota_exceeded	The plan's monthly allowance, plus the free buffer, is used up.	No: upgrade or wait
502	send_failed	It could not be sent or queued. details.interrupted says whether it may have been delivered.	Same key if interrupted is false
503	service_unavailable	Transactional sending is not enabled for the workspace yet.	No

Full details, including the sending limits, are in the transactional email API reference.

Supabase questions

How do I send email from a Supabase Edge Function?

Make a fetch request to your email provider's API from the function. With Warmerly that is a POST to /api/v1/transactional/emails with a bearer key, as in the function above.

Can I use Warmerly as Supabase Auth's SMTP server?

Not today: Supabase Auth sends over SMTP and Warmerly's transactional API is REST only.

Is there a Supabase package or SDK for Warmerly?

No. Warmerly's transactional API is one HTTP request, so there is nothing to install. The code on this page is the whole integration.

Can I send attachments?

Not yet. The send request takes from, to, cc, bcc, reply_to, subject, html or text, headers and tags. Attachments, SMTP relay, delivery webhooks and templates are not available today.

What if sending is throttled or the mail server cannot be reached?

If nothing was handed over, the email is queued rather than dropped. The request still answers 202 with a status of queued, and Warmerly retries it after 1, 5, 15 and 60 minutes, then hourly, for up to 24 hours.

Send your first Supabase email today

Create a free account, verify a sending domain and send a test. 5,000 emails a month free, no card.

Start sending free Continue with Google API docs

Or book a free 15-minute setup call →

Warming up

Send email from a Supabase Edge Function

Before you write any code

Four steps, the same in every framework. Warmerly is REST only today: no SMTP relay, webhooks, templates or attachments yet.

Step 1: Add and verify a sending domain

In Warmerly open Transactional email, add the domain you send from (for example mail.example.com), publish the DNS records it shows at your DNS provider, then verify. Use a domain or subdomain you do not use for cold outreach.

Step 2: Create a Sending API key

Under Transactional email, API keys, create a key with the Sending permission, optionally limited to that domain. It starts with wm_tx_ and is shown once, so copy it straight into your secrets store.

Step 3: Store the key as WARMERLY_TX_KEY

Set it as a function secret with the Supabase CLI: supabase secrets set WARMERLY_TX_KEY=wm_tx_xxxx. Then deploy with supabase functions deploy send-email.

Step 4: Add the code below and send a test

A successful request answers 202 with the email's id and a status of sent (or queued, which Warmerly retries for up to 24 hours). The free plan is 5,000 emails a month with no card.

The code

Copy these into your project. The request is the same one the API reference documents; nothing is hidden behind a package.

supabase/functions/send-email/index.ts

// supabase/functions/send-email/index.ts
const ENDPOINT = "https://app.warmerly.com/api/v1/transactional/emails";

type Payload = { to: string; subject: string; html?: string; text?: string; requestId: string };

Deno.serve(async (req: Request) => {
  if (req.method !== "POST") return new Response("Method not allowed", { status: 405 });

  const { to, subject, html, text, requestId } = (await req.json()) as Payload;

  const res = await fetch(ENDPOINT, {
    method: "POST",
    headers: {
      Authorization: `Bearer ${Deno.env.get("WARMERLY_TX_KEY")}`,
      "Content-Type": "application/json",
      // Reuse the same requestId when you retry the same message and it is sent once.
      "Idempotency-Key": requestId,
    },
    body: JSON.stringify({ from: "Acme <noreply@mail.example.com>", to, subject, html, text }),
  });

  const body = await res.json().catch(() => ({}));
  return new Response(JSON.stringify(body), {
    status: res.status === 202 ? 200 : 502,
    headers: { "Content-Type": "application/json" },
  });
});

Using it

Your app, or a Database Webhook

// From your app (supabase-js), or call it from a Database Webhook on insert.
const { data, error } = await supabase.functions.invoke("send-email", {
  body: {
    to: "jane@example.org",
    subject: "Welcome",
    text: "Thanks for signing up.",
    requestId: `welcome-${user.id}`,
  },
});

What to know about Supabase

Protect the function

Edge Functions require a valid JWT by default. Keep that on, and add your own checks about who may email whom, so the function cannot be used to send arbitrary mail.

Send on insert

To email when a row is inserted, add a Database Webhook that calls the function, and put the recipient and a stable id in the payload.

Supabase's own auth emails

Sign-up confirmation and password-reset messages come from Supabase Auth, which sends over SMTP. Warmerly has no SMTP relay yet, so this function is for the emails your own code triggers.

When the API does not send

Every refusal has a code in the response body, at error.code. These are the ones to handle, and whether to retry.

Error codes the send endpoint can return, what they mean and whether to retry
Status	Code	Meaning	Retry?
400	bad_request	Invalid body, or the From address is not on a verified sending domain.	No: fix the request
403	forbidden	The key is limited to a different sending domain.	No
403	sending_paused	Sending is paused for the workspace (bounce or complaint rate, or under review).	No: contact support
422	content_rejected	The message was refused by abuse screening.	No, not unchanged
429	rate_limited	The hourly or daily sending limit was reached.	Later
429	quota_exceeded	The plan's monthly allowance, plus the free buffer, is used up.	No: upgrade or wait
502	send_failed	It could not be sent or queued. details.interrupted says whether it may have been delivered.	Same key if interrupted is false
503	service_unavailable	Transactional sending is not enabled for the workspace yet.	No

Full details, including the sending limits, are in the transactional email API reference.

Supabase questions

How do I send email from a Supabase Edge Function?

Make a fetch request to your email provider's API from the function. With Warmerly that is a POST to /api/v1/transactional/emails with a bearer key, as in the function above.

Can I use Warmerly as Supabase Auth's SMTP server?

Not today: Supabase Auth sends over SMTP and Warmerly's transactional API is REST only.

Is there a Supabase package or SDK for Warmerly?

No. Warmerly's transactional API is one HTTP request, so there is nothing to install. The code on this page is the whole integration.

Can I send attachments?

Not yet. The send request takes from, to, cc, bcc, reply_to, subject, html or text, headers and tags. Attachments, SMTP relay, delivery webhooks and templates are not available today.

What if sending is throttled or the mail server cannot be reached?