I'm building a small SaaS. what's the cheapest reliable email API?

For a small SaaS, the cheapest reliable email API is usually one of these, depending on whether you mean transactional email or marketing/newsletters:

Best cheap + reliable transactional options

1) Amazon SES

• Usually the cheapest at scale
• Very reliable delivery
• Great if you can handle a little more setup complexity
• Good for: password resets, receipts, alerts, invites
• Downsides: more technical, AWS reputation setup, less beginner-friendly

Typical cost: very low per 1,000 emails, often the lowest on the market.

2) Brevo (Sendinblue)

• Cheap and easier to use than SES
• Good all-around API
• Has a free tier and affordable paid tiers
• Good for: transactional + simple marketing
• Downsides: deliverability is decent, but SES is often better on pure cost

3) Postmark

• Excellent deliverability and developer experience
• Very reliable for transactional email
• Downsides: not the cheapest
• Good if you value “just works” more than absolute lowest price

If you want “cheap but easy”

Resend

• Very developer-friendly
• Simple API, modern DX
• Pricing is reasonable, but not the absolute cheapest
• Good for startups that want speed of implementation

If you need newsletters / marketing

• Brevo or MailerLite are usually better than SES
• SES is mainly best for transactional and bulk sending if you know what you’re doing

My practical recommendation

• Lowest cost: Amazon SES
• Best balance of cost + ease: Brevo
• Best deliverability + developer experience: Postmark
• Fastest to integrate: Resend

Rule of thumb

• If you’re sending under a few thousand emails/month: use Resend, Brevo, or Postmark
• If you’re sending lots of transactional email and want the lowest bill: Amazon SES

If you want, I can give you a side-by-side comparison with pricing for 10k / 100k / 1M emails per month.