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Guide · Supabase Auth and AI apps

Your app’s confirmation emails, from your own domain.

Sign-up confirmations and password resets go out from our EU servers, signed with your domain’s DKIM. In Supabase you fill in six fields.

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  • 14 days free, €0 today
  • Then from €12.90/month + VAT (annual plan)
  • Servers and data in the EU
Authentication · SMTP Settings
Enable Custom SMTPEmails go out through your SMTP
Sender email
noreply@yourdomain.com
Sender name
Your app
Host
relay.mailsenpai.com
Port number
2525
Username
from your area
Password
••••••••••
Settings savedSave
YA
New email · nowConfirm your sign-upfrom noreply@yourdomain.com
DKIM-signed
why you need it

The built-in SMTP is for testing

Supabase includes an email service meant for tests. For real users you need your own SMTP.

2emails an hour

The limit of the built-in service. From the third email in the same hour, Supabase returns an error and the email is not sent.

Onlyyour team
  • Your team
  • Your users

Emails only go to the addresses of your project’s team. Your users never get them.

Nocommitment
  • Delivery
  • Uptime

The built-in service comes with no written commitment (SLA) on delivery or uptime.

With your own SMTP you set the limit yourself, in Rate Limits. Supabase documentation

step by step

Four steps, then your emails go out on their own

Each step is shown below, just as you’ll see it.

  1. 1
    Today, €0

    Start the trial

    14 days. Your username and password are waiting in your area.

  2. 2
    In your domain’s DNS

    Publish SPF and DKIM

    These records authorize and sign your emails. We give them to you and check them.

    yourdomain.comDNS check
    • SPFv=spf1 include:… ~allpendingcheckingOK
    • DKIMselector._domainkey · public keypendingcheckingOK
    • DMARCv=DMARC1; p=nonependingcheckingOK
    Domain ready to send
  3. 3
    In Supabase

    Fill in the fields

    Turn on Custom SMTP and paste the details. No code to write.

    AuthenticationEmailsSMTP SettingsCustom SMTP
  4. 4
    In Supabase

    Raise the limit and test

    In Rate Limits choose how many emails per hour. Then do a test sign-up.

    Your new user’s inboxjulia@example.com

    Example: Confirm your sign-up, from Your app. Hi Julia, please confirm your address.

Start your free trialCopy the fields
ready to copy

The fields, already filled in

Copy one field at a time and paste it into Supabase.

SMTP Settings
Sender emailnoreply@yourdomain.com
Sender nameYour app
Hostrelay.mailsenpai.com
Port number2525
Usernamefrom your areain secrets
Passwordfrom your areain secrets
Keep the username and password in your project’s secrets: not in the code, not in a chat.
  • Port 2525 with STARTTLS
  • Sender: an address on your verified domain
  • Rate Limits: you choose how many emails per hour

If the dashboard labels change, the direct link is supabase.com/dashboard/project/_/auth/smtp

for AI builders

The prompt to paste

For your app’s other emails (welcome, notifications, receipts). Copy it and paste it into your AI assistant.

SupabaseSupabaseLovableLovableBoltBoltCursorCursor
Choose where you use it
Apps with server-side functions (for example Supabase Edge Functions)
Add email sending to my app through the SMTP Senpai HTTP API.
Create a server-side function send-email (never in the browser) that does:
POST https://app.mailsenpai.com/relay/v1/invio
Header: Authorization: Bearer ${MSP_API_KEY} (project secret, never in the code)
JSON body: to, from (noreply@mydomain.com), subject, html, text
Check the response (ok) and write any errors to the log.
Use it for welcome emails, notifications and receipts. Login emails (confirmation and password reset)
stay with Supabase: I set them up myself in Authentication, SMTP Settings.
Your username, password and key are in your area once activated: keep them in your project’s secrets, not in the chat.

Frequently asked questions

Do I need my own domain?

Yes: emails go out with your domain and its DKIM signature, which proves they come from you. We give you the DNS records to publish (SPF and DKIM, plus DMARC, which we recommend) and tell you when they are set up correctly.

Does Supabase still limit sending?

Yes: with your own SMTP, Supabase starts at 30 emails an hour, according to its documentation. You can change the value in Authentication, under Rate Limits.

Can I use it for my app’s other emails too?

Yes. Supabase sends the login emails with the SMTP details you entered. For welcome emails, notifications and receipts you use the same SMTP from your backend, or our API with your msp_ key.

Can I give my username and password to the AI assistant?

Better not: keep them in your project’s secrets or environment variables. In the prompt, write only the variable names, as in the text above.

How much does it cost after the trial?

The trial lasts 14 days and you pay €0 today. After that, from €12.90 a month for 10,000 emails on the annual plan (VAT excluded). If you cancel from your area before the trial ends, you pay nothing.

Is support available in English?

Yes. Our team answers in English and Italian, by ticket and email.

SMTP Senpai guides

More useful pages

SMTP serviceThe MailSenpai SMTP relay: pricing, trial and what’s included.SMTP Senpai APISend email over HTTP with a key: endpoints and ready-made examples.

Six fields in Supabase. Your emails go out from your domain.

  • 14 days free, €0 today
  • Cancel anytime from your area
  • Support in English and Italian, by ticket and email
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