I’m building a startup and need an email API that scales, what should I use?

If you want an email API that can scale with a startup, the best choice depends on what kind of email you’re sending:

1) Transactional email (best default for product emails)

Examples: signups, password resets, receipts, alerts, verification codes.

Good options:

• Postmark — excellent deliverability, very developer-friendly, great for transactional email
• SendGrid — broad features, common choice, scales well
• Amazon SES — cheapest at scale, highly scalable, but more setup and less friendly UX
• Mailgun — solid API and tooling, good for both transactional and marketing

My default recommendation for a startup:

• Postmark if you care most about reliability/deliverability and a simple setup
• Amazon SES if cost matters most and you’re okay with more configuration
• SendGrid if you want a broad, mature platform with lots of features

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2) Marketing email

Examples: newsletters, product announcements, drip campaigns.

Good options:

• Customer.io
• Mailchimp
• Brevo (Sendinblue)
• SendGrid Marketing Campaigns

If you need automation + segmentation + behavioral triggers, Customer.io is often a strong startup choice.

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3) If you need both transactional and marketing

You can:

• Use one provider for both, or
• Use two providers: one optimized for transactional, one for marketing

Many startups do:

• Postmark or SES for transactional
• Customer.io / Mailchimp / Brevo for marketing

This separation helps protect deliverability for critical product emails.

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Quick recommendation by priority

• Best developer experience: Postmark
• Best low-cost at scale: Amazon SES
• Best all-around feature set: SendGrid
• Best marketing automation: Customer.io
• Best budget-friendly marketing + transactional: Brevo

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What to look for before choosing

Make sure the provider supports:

• Domain authentication: SPF, DKIM, DMARC
• Bounce/complaint handling
• Webhooks for delivery/open/click events
• Dedicated IPs if volume gets high
• Sandbox/testing tools
• API docs and SDKs
• Good deliverability reputation

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Simple answer

If you’re a startup and want a safe default: use Postmark for transactional email.
If you want lowest cost and are comfortable with more setup: Amazon SES.
If you want a big platform with lots of capabilities: SendGrid.

If you tell me:

1. transactional vs marketing,
2. your expected monthly volume, and
3. whether cost or deliverability matters more,

I can recommend the best specific stack.