Supabase email rate limit

I need to remember this, when testing Supabase, their SMTP servers block after a few emails (5? 10? 15? few, anyway), so after a while you’re trying things, email will stop working and it’ll start giving you an error message back:

Error: email rate limit exceeded

The frustrating part is that nothing looks broken. Signups appear to work, but confirmation emails never arrive, and only the error response tells you what happened.

Why this happens

Every Supabase project ships with a built-in email service so you can try auth flows immediately. That service is intentionally rate limited to a handful of emails per hour, and Supabase says it’s for testing only, not for production traffic.

When you’re iterating on a signup form you burn through that allowance fast. Sign up, delete the user, sign up again, test password reset… and you hit the wall.

How to fix

You need to use your SMTP server to go over that limit, in Settings → Authentication → SMTP Settings.

Enable “Custom SMTP” and fill in the credentials from your email provider. I use Resend, which gives you SMTP credentials out of the box:

Host: smtp.resend.com
Port: 465
Username: resend
Password: <your API key>
Sender email: auth@yourdomain.com

Any transactional email provider works the same way (Postmark, SES, Mailgun…). The sender address must belong to a domain you verified with that provider.

After saving, the rate limit is under your control: the dashboard exposes a “Rate Limits” section under Authentication where you can raise the emails-per-hour value.

One more thing that bit me: if you’re testing locally with the Supabase CLI, emails don’t go out at all by default. They’re captured by a local Inbucket/Mailpit inbox instead — run supabase status to get its URL and read the confirmation emails from there. No rate limit, no real emails sent.