Email Is Critical Infrastructure

For SaaS applications, email is not optional — it is a critical communication channel. Password resets, invoice receipts, account verifications, and system notifications all depend on reliable email delivery. If your emails land in spam, users cannot complete essential actions. At Nexis Limited, we manage email infrastructure across four SaaS products, delivering thousands of transactional emails daily.

Transactional vs Marketing Email

Transactional emails are triggered by user actions — password resets, order confirmations, invoice receipts, account notifications. Marketing emails are promotional — newsletters, announcements, product updates. These should use separate email infrastructure.

  • Use separate IP addresses and sending domains for transactional and marketing email. Marketing email reputation should not affect transactional deliverability.
  • Transactional emails should send immediately with high priority. Marketing emails can be batched and sent during optimal times.
  • Transactional emails typically do not require unsubscribe links (they are operational). Marketing emails legally require unsubscribe mechanisms.

Email Authentication (SPF, DKIM, DMARC)

Email authentication prevents spoofing and improves deliverability:

  • SPF (Sender Policy Framework): DNS record that specifies which servers are authorized to send email for your domain. Receiving servers check SPF to verify the sending server is legitimate.
  • DKIM (DomainKeys Identified Mail): Cryptographic signature on each email that verifies the email was sent by an authorized sender and has not been tampered with in transit.
  • DMARC (Domain-based Message Authentication): Policy that tells receiving servers what to do with emails that fail SPF and DKIM checks (quarantine, reject, or do nothing). Also provides reporting on authentication failures.

All three must be configured correctly for good deliverability. Most email service providers guide you through setup.

Email Service Providers

Transactional Email Services

  • Resend: Modern API-first email service with React Email template support. Excellent developer experience. Our preferred choice for new projects.
  • Postmark: Focused exclusively on transactional email with industry-leading delivery speed. No marketing email — ensures high reputation.
  • SendGrid: Comprehensive email platform supporting both transactional and marketing email. Mature and widely used.
  • AWS SES: Low-cost email sending with deep AWS integration. Requires more configuration than dedicated email services. Best for cost-sensitive, high-volume sending.

Email Template Management

React Email

Build email templates using React components. Write components in JSX, test with a local preview server, and render to HTML for sending. This provides a modern development experience for email templates — version control, component reuse, and TypeScript support.

Template Best Practices

  • Use inline CSS — many email clients strip external stylesheets and <style> blocks.
  • Use tables for layout — CSS Grid and Flexbox have inconsistent email client support.
  • Test across email clients (Gmail, Outlook, Apple Mail, Yahoo) using tools like Litmus or Email on Acid.
  • Include plain text versions for accessibility and deliverability.
  • Keep templates simple — complex layouts break across email clients.

Deliverability Best Practices

  • Warm up sending IPs: New IPs have no reputation. Start with low volume and gradually increase over 2-4 weeks.
  • Monitor bounce rates: Remove hard-bounced addresses immediately. High bounce rates damage sender reputation.
  • Monitor spam complaints: If users mark your email as spam, investigate and fix the cause. Complaint rates above 0.1% damage reputation.
  • Clean your email lists: Remove inactive addresses and validate email addresses at sign-up to prevent typos.
  • Send relevant content: Irrelevant emails get marked as spam. Segment your audience and personalize content.

Error Handling and Monitoring

  • Log every email sent with the template, recipient, and status.
  • Monitor delivery rates, bounce rates, and open rates.
  • Implement retry logic for temporary delivery failures.
  • Alert on delivery rate drops — they may indicate a reputation problem.
  • Provide support team tools to resend emails when users report non-delivery.

Conclusion

Email deliverability requires careful configuration and ongoing monitoring. Authenticate your domain with SPF, DKIM, and DMARC. Use a reputable email service provider. Separate transactional and marketing email infrastructure. Monitor deliverability metrics continuously. Reliable email is not something you set up once — it is infrastructure that requires ongoing attention.

Setting up email infrastructure? Our team configures email systems for SaaS applications.