Alright, first things first, we need an SMTP server to send those email notifications from Supabase. You have a few options here: you can set up your own SMTP server or go with services like SendGrid, Mailgun, or Amazon SES. Just sign up for one of these services and grab your SMTP credentials.

Next, head over to the Supabase dashboard and pick your project. Go to the Authentication section, then click on Settings. You'll see a tab called SMTP Configuration. Pop in the SMTP server details you got from Step 1:

• SMTP Host
• SMTP Port
• SMTP User
• SMTP Password

Make sure you set the right encryption (SSL/TLS) settings based on what your SMTP provider suggests.

Now, let's create a database function in Supabase to handle those email notifications using SQL. Go to the SQL editor and run this script:

CREATE OR REPLACE FUNCTION send_notification_email(user_id UUID, subject TEXT, message TEXT)
RETURNS void LANGUAGE plpgsql
AS $$
DECLARE
  user_email TEXT;
BEGIN
  SELECT email INTO user_email FROM auth.users WHERE id = user_id;
  
  PERFORM public.mail_send(user_email, subject, message);
END;
$$;

We need to set up a trigger that calls the function we just created. This trigger can respond to specific events like an insert or update. For example, to send an email when a new record is inserted:

CREATE TRIGGER user_insert_trigger
AFTER INSERT ON your_table_name
FOR EACH ROW
EXECUTE FUNCTION send_notification_email(NEW.id, 'Welcome!', 'Thank you for joining!');

Don't forget to replace your_table_name with the actual table name where you want the notifications.

Let's make sure the mail_send function is allowed to run in the database:

CREATE OR REPLACE FUNCTION public.mail_send(
  recipient_email text, 
  subject text, 
  body text
)
RETURNS void LANGUAGE plpgsql AS $$
BEGIN
  PERFORM 'curl -X POST -u "api:key-<your-api-key>" ' ||
          '--url https://api.mailgun.net/v3/<your-domain>/messages ' ||
          '-F from="Excited User <mailgun@your-domain>" ' ||
          '-F to=' || quote_literal(recipient_email) ||
          ' -F subject=' || quote_literal(subject) ||
          ' -F text=' || quote_literal(body);
END;
$$;

Make sure to replace the placeholders with your email service provider details and API keys.

Time to test! Manually trigger the event that should send an email notification. Check your inbox to see if the email came through. Fingers crossed!

Keep an eye on the system to make sure emails are being sent correctly. Look out for bounced emails or errors, and tweak things as needed to keep everything running smoothly.