The Complete Guide to Transactional Email in 2026

Transactional emails are the automated messages your application sends in response to user actions. Password resets, order confirmations, account notifications. They are expected, often time-sensitive, and critical to your application functioning properly.

This guide covers everything you need to implement transactional email correctly.

What Makes Email "Transactional"

Transactional emails are triggered by specific user actions or system events. The key characteristics:

• Triggered by action: The user did something that caused this email
• Expected: The recipient is waiting for this message
• Time-sensitive: Delayed delivery impacts user experience
• One-to-one: Sent to a single recipient, not batched

Common examples include:

• Password reset and email verification
• Two-factor authentication codes
• Order confirmations and receipts
• Shipping notifications
• Account security alerts
• Payment confirmations and invoices

Choosing a Transactional Email Service

You have several options for sending transactional email:

Dedicated Transactional Services

Postmark, Resend, and similar services focus specifically on transactional email. They optimize for deliverability and developer experience.

Unified Platforms

Sequenzy combines transactional and marketing email in one platform with native billing integrations. One sender reputation, one API, unified analytics.

Infrastructure Services

Amazon SES, SendGrid, and Mailgun provide email infrastructure at scale. More setup required, but flexible and cost-effective at volume.

Email Authentication

Authentication tells receiving servers that you are authorized to send from your domain. Three standards work together:

SPF (Sender Policy Framework)

A DNS TXT record listing servers authorized to send from your domain.

example.com.  TXT  "v=spf1 include:_spf.sequenzy.com ~all"

DKIM (DomainKeys Identified Mail)

Cryptographic signatures that prove the email was not modified in transit.

selector._domainkey.example.com.  TXT  "v=DKIM1; k=rsa; p=MIGf..."

DMARC (Domain-based Message Authentication)

Policy telling receivers what to do when SPF or DKIM fail.

_dmarc.example.com.  TXT  "v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com"

Basic Implementation

Here is a simple implementation using Sequenzy:

import { Sequenzy } from '@sequenzy/sdk';

const sequenzy = new Sequenzy({
  apiKey: process.env.SEQUENZY_API_KEY
});

// Send password reset email
async function sendPasswordReset(user: User, resetToken: string) {
  const resetLink = `https://app.example.com/reset?token=${resetToken}`;

  await sequenzy.send({
    to: user.email,
    template: 'password-reset',
    variables: {
      userName: user.name,
      resetLink,
      expiresIn: '1 hour'
    }
  });
}

Template Best Practices

Keep Templates Simple

Transactional emails should be clear and actionable. Avoid promotional clutter.

Use Plain Text Fallbacks

Always include a plain text version. Some recipients prefer it, and it helps deliverability.

Mobile-First Design

Over 60% of emails are opened on mobile. Use responsive layouts and large tap targets.

Clear Call to Action

One primary action per email. Make the button obvious and easy to click.

Handling Bounces and Complaints

Configure webhooks to handle delivery events:

// Express webhook handler
app.post('/webhooks/email', (req, res) => {
  const event = req.body;

  switch (event.type) {
    case 'bounce':
      // Mark email as invalid, stop sending
      markEmailInvalid(event.email, event.bounceType);
      break;

    case 'complaint':
      // User marked as spam, stop all email
      unsubscribeUser(event.email);
      break;

    case 'delivered':
      // Log successful delivery
      logDelivery(event.email, event.messageId);
      break;
  }

  res.status(200).send('OK');
});

Deliverability Checklist

• Set up SPF, DKIM, and DMARC correctly
• Use a dedicated sending domain (mail.example.com)
• Maintain clean recipient lists
• Handle bounces immediately
• Process unsubscribe requests promptly
• Monitor sender reputation
• Warm up new sending domains gradually

Common Mistakes

Mixing Transactional and Marketing

Sending newsletters through your transactional email infrastructure can hurt deliverability. Use separate streams or services.

Ignoring Bounces

Continuing to send to invalid addresses damages your sender reputation. Process bounces immediately.

No Plain Text Version

HTML-only emails can trigger spam filters and fail for some recipients.

Slow Delivery

Transactional emails should arrive within seconds. If your service has slow delivery times, users get frustrated.

Recommended Services

For most applications, we recommend:

• Sequenzy: Best for SaaS with billing integration needs. Unified transactional + marketing.
• Postmark: Best for pure deliverability focus. Industry-leading reliability.
• Resend: Best developer experience. React Email support.

See our full comparison of transactional email services for detailed analysis.