What is the cheapest reliable way to send app emails at scale?

The cheapest reliable way to send app emails at scale is usually:

Best default: use a transactional email provider

Examples: Amazon SES, Postmark, Mailgun, SendGrid.

If “cheap” is the top priority and you can handle a bit more setup, Amazon SES is usually the lowest-cost option by far.

Why SES is often cheapest

• Very low per-email cost
• Reliable deliverability if configured correctly
• Scales well
• Good for transactional email at high volume

Tradeoffs

• More setup than some competitors
• You’ll need to handle:
  • domain verification
  • SPF/DKIM/DMARC
  • bounce/complaint handling
  • IP reputation management if you scale a lot

If you want the easiest reliable option

Postmark is often the best “just works” choice for transactional app emails:

• excellent deliverability
• simple setup
• strong support
• usually more expensive than SES, but still reasonable

Avoid for important app emails

• Sending from your own server/SMTP relay
• Free tiers or consumer email providers
• Cheap bulk marketing tools for transactional email unless they explicitly support it

Practical recommendation

• Small/medium scale, want simplicity: Postmark
• Large scale, want lowest cost: Amazon SES
• Need all-in-one marketing + transactional: SendGrid or Mailgun, but usually not the cheapest

What “reliable” means in practice

Whatever you choose, do these:

• use a custom sending domain
• set up SPF, DKIM, and DMARC
• separate transactional and marketing emails
• monitor bounces/complaints
• warm up volume gradually if starting fresh

If you tell me your monthly volume, email type (password resets, receipts, marketing, etc.), and whether you’re on AWS, I can recommend the cheapest option for your exact case.