Supabase provides a Postgres database, auth, and Edge Functions (Deno-based serverless functions). Edge Functions are where you send emails: they run server-side, can access secrets, and respond to HTTP requests or database events.

This guide covers Edge Functions for email sending, database webhook triggers, and auth event handlers.

Create an Edge Function

supabase functions new send-email

This creates supabase/functions/send-email/index.ts.

Email Sending Function

supabase/functions/send-email/index.ts

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

const { to, subject, body } = await req.json();

if (!to || !subject || !body) {
  return Response.json({ error: "to, subject, and body required" }, { status: 400 });
}

const response = await fetch("https://api.sequenzy.com/v1/transactional/send", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${Deno.env.get("SEQUENZY_API_KEY")}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({ to, subject, body }),
});

if (!response.ok) {
  return Response.json({ error: "Failed to send" }, { status: 500 });
}

const result = await response.json();
return Response.json(result);
});

supabase/functions/send-email/index.ts

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

const { to, subject, html } = await req.json();

if (!to || !subject || !html) {
  return Response.json({ error: "to, subject, and html required" }, { status: 400 });
}

const response = await fetch("https://api.resend.com/emails", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${Deno.env.get("RESEND_API_KEY")}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    from: "Your App <noreply@yourdomain.com>",
    to, subject, html,
  }),
});

if (!response.ok) {
  return Response.json({ error: "Failed to send" }, { status: 500 });
}

const result = await response.json();
return Response.json(result);
});

supabase/functions/send-email/index.ts

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

const { to, subject, html } = await req.json();

if (!to || !subject || !html) {
  return Response.json({ error: "to, subject, and html required" }, { status: 400 });
}

const response = await fetch("https://api.sendgrid.com/v3/mail/send", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${Deno.env.get("SENDGRID_API_KEY")}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    personalizations: [{ to: [{ email: to }] }],
    from: { email: "noreply@yourdomain.com" },
    subject,
    content: [{ type: "text/html", value: html }],
  }),
});

if (!response.ok) {
  return Response.json({ error: "Failed to send" }, { status: 500 });
}

return Response.json({ sent: true });
});

Set Secrets

supabase secrets set SEQUENZY_API_KEY=sq_your_key

Deploy

supabase functions deploy send-email

Call from Your App

import { createClient } from "@supabase/supabase-js";
 
const supabase = createClient(SUPABASE_URL, SUPABASE_ANON_KEY);
 
// Call the edge function
const { data, error } = await supabase.functions.invoke("send-email", {
  body: {
    to: "user@example.com",
    subject: "Welcome!",
    body: "<h1>Welcome!</h1><p>Your account is ready.</p>",
  },
});

Database Webhook Trigger

Send an email when a new row is inserted. Create a webhook function:

// supabase/functions/on-new-order/index.ts
Deno.serve(async (req) => {
  const payload = await req.json();
  const { record } = payload; // The new row
 
  const response = await fetch("https://api.sequenzy.com/v1/transactional/send", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${Deno.env.get("SEQUENZY_API_KEY")}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      to: record.email,
      subject: "Order confirmed!",
      body: `<h1>Thanks for your order!</h1><p>Order #${record.id} is confirmed.</p>`,
    }),
  });
 
  return Response.json({ sent: response.ok });
});

Then in the Supabase dashboard: Database > Webhooks > Create webhook pointing to this function, triggered on INSERT to your orders table.

Auth Email Trigger

Send a welcome email when a user signs up:

// supabase/functions/on-auth-signup/index.ts
Deno.serve(async (req) => {
  const payload = await req.json();
  const { email, user_metadata } = payload.record;
 
  await fetch("https://api.sequenzy.com/v1/transactional/send", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${Deno.env.get("SEQUENZY_API_KEY")}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      to: email,
      subject: `Welcome, ${user_metadata?.name ?? "there"}!`,
      body: `<h1>Welcome!</h1><p>Your account is ready.</p>`,
    }),
  });
 
  return Response.json({ sent: true });
});

Going to Production

1. Verify Your Domain

Add SPF, DKIM, DMARC DNS records.

2. Use Secrets, Not Env Vars

supabase secrets set SEQUENZY_API_KEY=sq_your_key

3. Add Error Handling

Edge Functions have a 60-second timeout. Email API calls are fast, but add error handling for reliability.

Beyond Transactional

Sequenzy handles transactional sends, marketing campaigns, automated sequences, and subscriber management from one API. Native Stripe integration for SaaS.

Wrapping Up

Edge Functions for server-side email sending
Database webhooks to trigger emails on row changes
Auth triggers for welcome emails on signup
Supabase client to invoke functions from your app

Pick your provider, deploy a function, and start sending.