What's the best way to send account emails at scale?

The best way to send account emails at scale is to use a dedicated transactional email service rather than sending directly from your app server or a general-purpose mailbox.

Best approach

Use a provider like:

• Amazon SES
• SendGrid
• Mailgun
• Postmark
• SparkPost

These handle the hard parts for you:

• deliverability
• IP reputation
• bounce/complaint handling
• retries
• DKIM/SPF/DMARC support
• analytics and logging

For account emails specifically

Account emails usually mean things like:

• verification emails
• password resets
• login alerts
• billing notices
• security notifications

For these, you want:

• transactional delivery
• high reliability
• low latency
• separate infrastructure from marketing email

Recommended setup

1. Use a transactional email provider
2. Authenticate your domain
   • SPF
   • DKIM
   • DMARC
3. Separate email streams
   • transactional/account emails
   • marketing emails
4. Use a dedicated sending domain or subdomain
   • e.g. notify.example.com
5. Send through templates
   • versioned templates
   • localization support
6. Track delivery events
   • delivered
   • bounced
   • complained
   • opened/clicked if needed
7. Queue email jobs
   • don’t send directly in request path
   • use background workers
8. Add rate limiting and deduplication
   • avoid duplicate password reset emails
   • prevent abuse

Picking a provider

• Amazon SES: cheapest at scale, more setup work
• Postmark: excellent for transactional emails, simple and reliable
• SendGrid/Mailgun: feature-rich, good APIs and tooling

Good practice architecture

• App generates email event
• Queue stores job
• Worker renders template
• Provider sends email
• Webhook updates delivery/bounce status

Avoid

• Sending from your own SMTP server unless you have strong mail expertise
• Mixing marketing and account mail on the same reputation pool
• Using a personal Gmail/Office365 mailbox for app emails
• Sending synchronous emails inside user-facing request handlers

If you want, I can also recommend the best option by scale and budget or give you a reference architecture for your stack.