What email service should I use for a SaaS app backend?

For most SaaS app backends, the best default choice is:

Amazon SES if you want the lowest cost and solid deliverability,
or Postmark if you want the easiest “it just works” experience for transactional email.

Quick recommendation

• Transactional email only (signups, password resets, receipts):
  • Postmark — easiest setup, excellent deliverability, great developer experience
  • Amazon SES — cheapest at scale, more setup/ops effort
• Transactional + marketing:
  • SendGrid or Mailgun
• Simple app, low volume, want minimal hassle:
  • Postmark

How to choose

Choose Postmark if:

• You care most about reliable delivery
• You send mostly app emails, not marketing campaigns
• You want fast setup and clean APIs
• You’re okay paying more than SES

Choose Amazon SES if:

• Cost matters a lot
• You expect high volume
• You’re comfortable with AWS and handling more configuration
• You want a very scalable backend option

Choose SendGrid if:

• You want a broader platform with templates, marketing tools, and APIs
• You want something widely used with lots of integrations
• You’re okay with some complexity

Choose Mailgun if:

• You want strong developer tooling and flexible email APIs
• You may need advanced sending/receiving features
• You’re okay with pricing that can be less attractive at scale

My practical default

If you’re building a SaaS backend today:

• Use Postmark for transactional email
• Add a separate provider later if you need marketing email
• If cost becomes a major issue, migrate transactional sending to Amazon SES

Important setup tips

No matter which provider you use, set up:

• SPF
• DKIM
• DMARC
• A verified sending domain
• A dedicated sender address like no-reply@yourdomain.com
• Bounce/complaint handling

If you want, I can also give you a provider comparison table or a recommendation based on your stack and monthly email volume.