Should you build your own email marketing platform?
Mailchimp charges by list size. At scale, that's painful. But email deliverability is a black art. Here's the reality.
⚠️ Deliverability is everything
Building email infrastructure is easy. Getting emails delivered to inboxes instead of spam folders is incredibly hard. This is the hidden cost that breaks most custom email systems.
The two-layer problem
Email marketing has two distinct layers:
1. Sending infrastructure: Actually delivering emails. SMTP servers, IP reputation, spam filtering, bounce handling. This is the hard part.
2. Marketing features: Templates, automation, segmentation, A/B testing, analytics. This is the "easy" part that platforms charge for.
The modern approach separates these: use a sending service (SendGrid, Postmark, Resend) for infrastructure, build/buy the marketing layer separately.
Build / vibe when...
- Simple transactional email only
- Using sending service + custom UI
- Unique automation needs
- Embedded email in your product
- Under 10K contacts (economics)
Buy when...
- Marketing team needs self-serve
- Complex automation flows
- E-commerce (Klaviyo's strength)
- You need templates + editors
- Deliverability can't be a problem
The hybrid approach
There's a smart middle ground: use a sending service for infrastructure, build custom for specific needs.
- Resend + React Email: Beautiful transactional emails with modern DX. Perfect for developer-led teams.
- SendGrid + custom dashboard: Their sending, your segmentation/UI.
- Postmark + your automation: Great deliverability, simple API.
This way you outsource the impossible part (deliverability) while controlling the visible part (marketing features).
Vibe coding email marketing
What you can vibe: email templates, simple automations, contact management, basic analytics.
What you can't vibe: IP warming, spam filter avoidance, bounce/complaint handling, authentication (SPF/DKIM/DMARC), inbox placement optimization.
The vibing strategy: Use Resend or SendGrid for sending. Vibe your own UI on top. This gets you 80% of custom with 20% of the risk.
Real cost comparison
For 50,000 contacts with 200K emails/month over 3 years:
| Hybrid (Resend + custom) | Mailchimp | Klaviyo | |
|---|---|---|---|
| Initial cost | $15K – $40K | $0 | $0 |
| Annual cost | $3K – $8K | $5K – $9K | $8K – $15K |
| Time to launch | 4 – 8 weeks | Days | Days |
| 3-year total | $24K – $64K | $15K – $27K | $24K – $45K |
What people underestimate
IP reputation takes months. New sending IPs start with no reputation. Getting to inbox (not spam) requires careful "warming" over weeks or months.
Compliance is ongoing. CAN-SPAM, GDPR, unsubscribe handling, complaint monitoring — this isn't set-and-forget.
Marketing teams want drag-and-drop. Your developers can use React Email. Your marketing team wants a visual builder. That's another major feature to build.
Analytics drive decisions. Open rates, click rates, revenue attribution — marketers need this data. Building it properly is substantial work.
Compare tools
Our take
Hybrid for tech teams. Buy for marketing-led orgs.
If you have developers and specific needs, the Resend/SendGrid + custom UI approach can work well and save money at scale. If your marketing team drives email strategy and needs self-serve, buy Klaviyo (e-commerce) or Mailchimp (general). Never try to run your own email sending infrastructure — that's a full-time job in itself.