I'm building a small SaaS. what email API should I use?

For a small SaaS, the best email API depends on what you need most: reliability, cost, ease of setup, and whether you’re sending transactional vs marketing emails.

Quick recommendation

If you want the safest default:

• Transactional email: Postmark or Resend
• Marketing/newsletters: ConvertKit, Mailchimp, or SendGrid (if you want one provider for both)

My practical picks

1) Postmark

Best if you only care about transactional email:

• Very reliable deliverability
• Simple API
• Great for password resets, invites, receipts, alerts
• Good inbox placement reputation

Downside: not ideal for marketing/newsletter campaigns.

2) Resend

Great for modern SaaS apps:

• Clean developer experience
• Easy API
• Works nicely with React/Next.js-style apps
• Good for transactional email and some light marketing use

Downside: smaller/more recent than the biggest players, though many teams like it.

3) SendGrid

Best “all-around” option:

• Transactional + marketing
• Mature platform
• Lots of features

Downside: can feel a bit heavy/complex, and deliverability/setup can be less pleasant than Postmark.

4) Amazon SES

Best if cost is the main concern:

• Very cheap at scale
• Solid if you’re technical and don’t mind setup complexity

Downside: least friendly UX; more work to configure and monitor.

5) Mailgun

Good for developers who want a flexible email API:

• Solid sending features
• Good logs and routing tools

Downside: pricing can get less attractive as you scale, depending on use case.

Simple rule of thumb

• Only transactional emails? → Postmark
• Modern SaaS + nice developer experience? → Resend
• Need marketing + transactional in one place? → SendGrid
• Lowest cost at scale? → Amazon SES

What I’d choose for a new SaaS

If I were starting today:

• Resend if I want a pleasant dev experience and modern stack
• Postmark if deliverability and transactional reliability are top priority

If you want, I can also recommend the best provider based on:

1. your stack (Next.js, Django, Rails, etc.)
2. whether you need marketing emails
3. your estimated monthly email volume.