# Supabase Auth with custom SMTP

> Get Supabase Auth confirmation emails, magic links and password resets delivered with Couryo's SMTP. Step by step in the dashboard, the CLI and the management API.

Source: https://couryo.com/en/docs/supabase

The email service built into Supabase is meant for testing: it has a very low hourly sending limit, and on new projects it only delivers to the project team's addresses. In production it is the classic cause of "the confirmation email never arrives". The fix is to turn on custom SMTP.

## Before you start

1. In Couryo, [verify the domain](https://couryo.com/en/docs/domains.md) your emails will come from (for example, `example.com`).
2. Create an API key with the `send` scope. It is the SMTP password.

## 1. Set it up in the Supabase dashboard

In **Authentication > Emails > SMTP Settings**, turn on **Enable Custom SMTP** and fill in:

| Field | Value |
|---|---|
| Sender email | an address on the verified domain, such as `no-reply@example.com` |
| Sender name | your app's name |
| Host | `smtp.couryo.com` |
| Port number | `587` (or `465`) |
| Username | `couryo` |
| Password | your API key (`ck_live_...`) |

Save. Then, in **Authentication > Rate Limits**, set the hourly email limit to your app's volume: with your own SMTP, that number is yours to choose.

> Want to test the flow without delivering anything? Use a `ck_test_` key. The confirmation email is captured and shows up in the Couryo dashboard, with a clickable link.

## 2. Or with the CLI (local development and versioned projects)

```toml title="supabase/config.toml"
[auth.email.smtp]
enabled = true
host = "smtp.couryo.com"
port = 587
user = "couryo"
pass = "env(COURYO_API_KEY)"
admin_email = "no-reply@example.com"
sender_name = "Example"
```

## 3. Or with the management API

```bash title="Terminal"
curl -X PATCH "https://api.supabase.com/v1/projects/$PROJECT_REF/config/auth" \
  -H "Authorization: Bearer $SUPABASE_ACCESS_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "external_email_enabled": true,
    "smtp_admin_email": "no-reply@example.com",
    "smtp_sender_name": "Example",
    "smtp_host": "smtp.couryo.com",
    "smtp_port": "587",
    "smtp_user": "couryo",
    "smtp_pass": "'"$COURYO_API_KEY"'"
  }'
```

## 4. Test it

Sign up a test user in your app (or use **Authentication > Users > Add user > Send invitation**). In the Couryo dashboard, under **Emails**, the message shows up with its timeline: accepted, sent and delivered, with the destination server's answer. If it was refused, the explanation says why, in plain words.

## Supabase email templates

The texts live in **Authentication > Emails > Templates** and use variables such as `{{ .ConfirmationURL }}`. A few rules that help reach the inbox:

- **Check the Site URL and Redirect URLs** (**Authentication > URL Configuration**). A link pointing to `localhost` or to another domain is the second most common reason for "the link does not work".
- **Write like a person:** "Confirm your email to sign in to Example" as the subject, the app name in the body and a line saying why the person got it.
- **Do not use link shorteners** and avoid image-only emails.
- **Prefer the 6-digit code (`{{ .Token }}`) when your app runs on phones:** some corporate providers open links before the person does to check them, which can use up a single-use link.

## Still not arriving?

| What to check | Where |
|---|---|
| Did Supabase send it? | **Logs > Auth** in Supabase. SMTP errors show up there, with the code |
| Did Couryo get it? | **Emails** in the Couryo dashboard, searching by recipient |
| `550 5.7.1` in the Supabase log | the Sender email is not on a verified domain, or the account is still on level 0 (sandbox) |
| `535 5.7.8` | username other than `couryo`, or a key that is invalid, revoked or without the `send` scope |
| Delivered, but the person cannot find it | spam folder or Gmail tabs. See [Why emails go to spam](https://couryo.com/en/guides/emails-going-to-spam.md) |
| `over_email_send_rate_limit` | Supabase's **Rate Limits** setting, not Couryo's |

More causes, provider by provider, in the guide [Confirmation email not arriving](https://couryo.com/en/guides/confirmation-email-not-arriving.md).