Email

There are two paths and they are easy to confuse.

Your mail goes through the Resend API from src/lib/email.ts: receipts, welcome messages, anything your app decides to send.

Supabase's mail is the magic link and the confirmation. Supabase sends that, not you, so it has to be told to send it through Resend over SMTP.

Your mail#

import { sendEmail } from "@/lib/email";

await sendEmail({
  to: user.email,
  subject: "You're in",
  html: "<p>Everything is ready.</p>",
});

Templates are plain functions that return { subject, html }. No template engine, no MJML build step. If you want a designer's HTML, paste it in.

Supabase's mail#

Under Project settings, Authentication, SMTP:

Host      smtp.resend.com
Port      465
User      resend
Password  your Resend API key
Sender    the same address as EMAIL_FROM

Then rewrite the three templates as described in Authentication. The default templates will not sign anyone in.

Deliverability#

Three DNS records decide whether your mail lands or goes to spam. Resend gives you all three when you add a domain:

They sit on a send subdomain, so they do not collide with existing email forwarding on your apex.

Swapping provider#

src/lib/email.ts is about forty lines and exports one function. Postmark, SES and Loops all take the same shape. Change that file; nothing else imports the SDK.