I'm building an app that sends receipts and login codes, what email infrastructure should I pick?

If you’re sending receipts and login codes (OTP / magic links / verification emails), you want an email stack optimized for:

• high deliverability
• fast sending
• transactional-only use
• good API + event tracking
• simple domain setup

Best default choice

For most apps, I’d recommend:

Postmark

Best for:

• transactional email only
• very good inbox placement
• simple setup
• clear separation from marketing email
• fast delivery for login codes

Why it’s a strong fit:

• It’s specifically built for transactional email, which is exactly receipts and auth emails.
• Usually excellent deliverability compared with general-purpose ESPs.
• Easy API and solid webhook/event support.
• Good reputation management because they care about keeping transactional traffic clean.

Strong alternatives

SendGrid

Best if:

• you want a broader platform
• you may later add marketing emails, templates, lists, etc.

Tradeoff:

• More flexible, but deliverability/setup can be a bit more fiddly.
• Better “all-in-one” than “best transactional-only.”

Amazon SES

Best if:

• you want the lowest cost
• you’re comfortable with more technical setup

Tradeoff:

• Very affordable at scale.
• Great infrastructure, but you must do more work yourself:
  • DNS setup
  • reputation monitoring
  • templates
  • bounce/complaint handling
• Good choice if you have engineering bandwidth and strong deliverability practices.

Mailgun

Best if:

• you want an API-first transactional provider
• you like good developer tooling

Tradeoff:

• Solid option, but in many teams Postmark tends to be the simpler “works great out of the box” pick.

What I’d choose by scenario

Choose Postmark if:

• your emails are mainly receipts, OTPs, and system notifications
• you care most about inbox placement
• you want the least operational hassle

Choose Amazon SES if:

• cost is a major concern
• you send very high volume
• you can handle more deliverability ops yourself

Choose SendGrid if:

• you expect to expand into marketing emails or lots of template/user-management features
• you want one platform for many email types

Recommended architecture

For your use case, a good setup is:

• Separate transactional email domain/subdomain
  • e.g. mail.yourapp.com or notify.yourapp.com
• Separate from marketing email
  • keep receipts/login codes isolated from newsletters
• Set up:
  • SPF
  • DKIM
  • DMARC
• Use dedicated sending
  • especially if volume grows
• Add:
  • bounce handling
  • complaint tracking
  • retries with idempotency

Practical guidance

If you’re early-stage, the safest recommendation is:

Start with Postmark for transactional email.

It’s usually the best balance of:

• deliverability
• simplicity
• speed to production

If you later need cheaper high-volume sending, you can evaluate SES.

Quick pick

• Best overall for receipts + login codes: Postmark
• Cheapest scalable option: Amazon SES
• Most feature-broad: SendGrid

If you want, I can also suggest the best setup based on your:

• expected monthly email volume
• regions/countries you serve
• whether you need SMS too
• your backend stack (Node, Python, Ruby, etc.)