Indie Dev Email Marketing Complete Guide — Automate with Resend Supabase

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Indie Dev Email Marketing Complete Guide — Automate with Resend × Supabase

Email drives higher conversions than social media. Here's how indie developers can automate email marketing using Resend and Supabase.

Why Email Matters

Channel	Avg Open Rate	Click Rate	Conversion Rate
Email	21-28%	2-5%	2-4%
Twitter/X	0.5-1%	0.1-0.3%	0.1-0.5%
Push Notifications	4-8%	0.5-1%	0.5-1%

Unlike social media, your email list is an asset you own — algorithm changes can't take it away.

Sending Email with Resend

// Supabase Edge Function: send-email
import { Resend } from 'npm:resend';

const resend = new Resend(Deno.env.get('RESEND_API_KEY')!);

Deno.serve(async (req) => {
  const { to, subject, html } = await req.json();

  const { data, error } = await resend.emails.send({
    from: 'Jibun AI <hello@jibun.ai>',
    to,
    subject,
    html,
  });

  if (error) return Response.json({ error }, { status: 400 });
  return Response.json({ id: data?.id });
});

Welcome Sequence Design

Sign-up → Day 0: Welcome (feature overview)
        → Day 3: Use cases (concrete examples)
        → Day 7: Tips (advanced features)
        → Day 14: Community introduction
        → Day 30: Paid plan offer

Automate with Supabase

CREATE TABLE email_sequences (
  id UUID DEFAULT gen_random_uuid() PRIMARY KEY,
  user_id UUID REFERENCES auth.users(id),
  sequence_name TEXT NOT NULL,
  step INTEGER NOT NULL DEFAULT 0,
  scheduled_at TIMESTAMPTZ NOT NULL,
  sent_at TIMESTAMPTZ,
  created_at TIMESTAMPTZ DEFAULT NOW()
);

CREATE OR REPLACE FUNCTION create_welcome_sequence()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO email_sequences (user_id, sequence_name, step, scheduled_at)
  VALUES
    (NEW.id, 'welcome', 0, NOW()),
    (NEW.id, 'welcome', 1, NOW() + INTERVAL '3 days'),
    (NEW.id, 'welcome', 2, NOW() + INTERVAL '7 days'),
    (NEW.id, 'welcome', 3, NOW() + INTERVAL '14 days'),
    (NEW.id, 'welcome', 4, NOW() + INTERVAL '30 days');
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER on_user_created
  AFTER INSERT ON auth.users
  FOR EACH ROW EXECUTE FUNCTION create_welcome_sequence();

-- Trigger sequence processing hourly via pg_cron
SELECT cron.schedule(
  'process-email-sequences',
  '0 * * * *',
  $$
    SELECT net.http_post(
      url := 'https://<project>.supabase.co/functions/v1/process-email-sequences',
      headers := '{"Authorization": "Bearer <service_role_key>"}'::jsonb,
      body := '{}'::jsonb
    );
  $$
);

Email Templates with React Email

import {
  Html, Head, Body, Container, Text, Button, Hr
} from 'npm:@react-email/components';

export function WelcomeEmail({ name }: { name: string }) {
  return (
    <Html>
      <Head />
      <Body style={{ fontFamily: 'sans-serif', backgroundColor: '#f4f4f5' }}>
        <Container style={{ maxWidth: 600, margin: '40px auto', padding: '0 20px' }}>
          <Text style={{ fontSize: 24, fontWeight: 'bold', color: '#1e1b4b' }}>
            Welcome, {name}!
          </Text>
          <Text style={{ color: '#374151', lineHeight: 1.7 }}>
            Thanks for signing up for Jibun AI — your AI Life Management app.
          </Text>
          <Button
            href="https://my-web-app-b67f4.web.app/"
            style={{
              backgroundColor: '#4f46e5',
              color: '#fff',
              padding: '12px 24px',
              borderRadius: 6,
              fontWeight: 'bold',
            }}
          >
            Get Started →
          </Button>
          <Hr />
          <Text style={{ fontSize: 12, color: '#9ca3af' }}>
            <a href="{{ unsubscribe_url }}">Unsubscribe</a>
          </Text>
        </Container>
      </Body>
    </Html>
  );
}

Segmented Campaigns

async function sendSegmentedEmail(userId: string) {
  const { data: user } = await supabase
    .from('user_profiles')
    .select('plan, usage_count, last_active')
    .eq('user_id', userId)
    .single();

  if (!user) return;

  const isDormant = new Date(user.last_active) < new Date(Date.now() - 14 * 24 * 3600 * 1000);
  const isHighEngagement = user.usage_count > 50;
  const isFree = user.plan === 'free';

  let template: string;
  let subject: string;

  if (isDormant) {
    subject = 'We miss you — come back';
    template = 'reactivation';
  } else if (isHighEngagement && isFree) {
    subject = "You're a power user — here's an upgrade offer";
    template = 'upgrade_offer';
  } else {
    subject = 'This week\'s tips & tricks';
    template = 'weekly_tips';
  }

  await sendEmail({ userId, subject, template });
}

Tracking Opens and Clicks

CREATE TABLE email_events (
  id UUID DEFAULT gen_random_uuid() PRIMARY KEY,
  email_id TEXT NOT NULL,
  event_type TEXT NOT NULL,  -- 'sent', 'opened', 'clicked', 'bounced', 'unsubscribed'
  user_id UUID REFERENCES auth.users(id),
  metadata JSONB,
  created_at TIMESTAMPTZ DEFAULT NOW()
);

-- Open rate by template (last 30 days)
SELECT
  template_name,
  COUNT(*) FILTER (WHERE event_type = 'sent') AS sent,
  COUNT(*) FILTER (WHERE event_type = 'opened') AS opened,
  ROUND(
    COUNT(*) FILTER (WHERE event_type = 'opened')::NUMERIC /
    NULLIF(COUNT(*) FILTER (WHERE event_type = 'sent'), 0) * 100, 1
  ) AS open_rate_pct
FROM email_events
WHERE created_at >= NOW() - INTERVAL '30 days'
GROUP BY template_name;

Summary

Resend × Supabase email marketing delivers:

Welcome sequences that automate onboarding
Segmented campaigns for maximum engagement
pg_cron integration — fully automated, no external tools
Open/click tracking for data-driven optimization

Even solo indie developers can run enterprise-grade email marketing.

Building an AI Life Management app with Flutter × Supabase at 自分株式会社. Sharing indie dev insights every week.

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