Monitoring Email Deliverability: When Transactional Emails Stop Arriving

Your user clicks "Forgot Password." They wait for the reset email. It never arrives. They try again. Still nothing. They contact support — or worse, they give up and leave.

Transactional email failures are invisible to most monitoring setups. Your application sends the email, your email provider accepts it, and monitoring shows everything's green. But the email never reaches the inbox.

Why Transactional Emails Fail

Deliverability Issues

• Your sending domain's reputation dropped
• You landed on a blocklist
• SPF/DKIM/DMARC records are misconfigured
• You're sending from a shared IP with a bad reputation

Provider Issues

• Your email provider (SendGrid, SES, Postmark) has an outage
• Rate limits exceeded
• Account suspended for policy violation
• API credentials expired

Content Issues

• Spam filters flag your emails
• HTML rendering breaks in certain email clients
• Links in the email point to broken URLs

What to Monitor

Email Sending Health

• Monitor your email provider's API endpoint (HTTP check)
• Track send success rate
• Monitor bounce rates and complaint rates
• Alert on any delivery error spikes

Deliverability Metrics

• Open rates for transactional emails (sudden drops indicate inbox placement issues)
• Bounce rates by type (hard vs soft)
• Spam complaint rates
• Blocklist status for your sending IPs

DNS Records

• SPF record validity
• DKIM key validity
• DMARC policy configuration

Critical Email Flows

Monitor the most important transactional emails:

• Password reset delivery
• Magic link login delivery
• Order confirmation delivery
• Account verification delivery

Practical Monitoring Setup

1. Email Provider API Health

HTTP monitor on your email provider's API endpoint. If SendGrid's API is down, no emails are sending.

2. Send Pipeline Heartbeat

After your email sending job processes its queue, ping a heartbeat monitor. If the heartbeat stops, the pipeline is stuck.

3. Delivery Rate Monitoring

Track your email provider's delivery dashboard. Set up alerts for:

• Delivery rate drops below 95%
• Bounce rate exceeds 3%
• Spam complaint rate exceeds 0.1%

4. End-to-End Test

Periodically send a test email through your full pipeline and verify it arrives in a monitored inbox.

The Email Monitoring Checklist

• Email provider API monitored (30-second intervals)
• Send pipeline heartbeat active
• Delivery rate alerts configured
• Bounce rate alerts configured
• SPF/DKIM/DMARC records verified
• Blocklist monitoring for sending IPs
• End-to-end delivery test (daily)

Your transactional emails are as critical as your API. Monitor them accordingly.