If you’re building an app and sending emails… you’re probably making at least one of these mistakes.

In this episode, I sit down with Chris Pennington from Resend to break down email deliverability — what it actually means, why your emails end up in spam, and the simple fixes most developers overlook.

We go beyond theory and cover real-world examples, including mistakes I’ve personally made in my own app.

🚀 What You’ll Learn
→ Why you should NEVER send from your root/apex domain
→ How to isolate sending reputation with subdomains
→ The fake email testing trap that tanks domain reputation
→ Webhooks & observability to catch issues before they spiral
→ Email threading — how to stop auth emails from chaining together
→ Idempotency keys to prevent double-sending on retries
→ Transactional vs. broadcast emails — and when to use each
→ Resend's new AI skills for React Email & best practices

🧠 Key Takeaway
✓ Email deliverability isn’t just infrastructure — it’s behavior.
✓ If you don’t send emails the right way, email clients will treat you like a spammer even if you’re legit.

🔗 Links mentioned:
- Resend: https://resend.com
- React Email: https://react.email
- Resend Docs: https://resend.com/docs
- Resend Skills: https://resend.com/docs/resend-skill
- Test email addresses: bounced@resend.dev / delivered@resend.dev

👨‍💻 About Chris
Chris Pennington is a DX Engineer at Resend, helping developers build better email systems with modern tooling and best practices. Connect with him on X → https://x.com/cpenned

⏱️ Chapters:
00:00 – Intro & who is Chris Pennington?
02:00 – What is Resend & why devs love it
05:30 – React Email origins (the surprising backstory)
09:30 – The 5 general deliverability tips
11:30 – Tip 1: Always use subdomains
20:00 – Tip 2: Separate auth vs. marketing sending
30:00 – Tip 3: Webhooks & real-time observability
35:00 – Tip 4: Stop using fake test emails
37:00 – Tip 5: Fix email threading with custom headers
38:00 – Tip 6: Idempotency keys explained
50:00 – Broadcasts, segments & unsubscribe flows
1:00:00 – Wrap up & what's next from Resend

💬 Let me know in the comments:
What’s the biggest issue you’ve had with email in your app?

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#email #webdevelopment #resend #saas #develope

Hamed Bahram

A developer-focused conversation with a DX engineer from Resend covering 10 practical tips for improving email deliverability. General tips include: using subdomains instead of apex domains to isolate sending reputation, warming up domains gradually and predictably, sending only to engaged users, using topic-based segmentation for granular opt-in control, and keeping email size under 102KB. Developer-specific tips cover: respecting API rate limits, setting up webhooks for real-time observability, using Resend's test email suite (e.g. bounced@resend.dev) instead of fake addresses that cause real bounces, preventing unwanted email threading with custom headers, and implementing idempotency keys to avoid duplicate sends during retry logic. The session also includes a live walkthrough of the Resend dashboard covering domains, warm-up calculators, audiences, segments, and topics.

Why Your Emails Go to Spam (And How to Fix It) ft. Chris Pennington