Email Testing Checklist for QA Teams

Email testing is often treated as an afterthought, but it is critical for user experience. This checklist covers the essential tests QA teams should perform on email flows.

Delivery testing

Basic delivery: Does the email arrive at all within 30 seconds?
Multiple recipients: Does delivery work for CC and BCC recipients?
Large attachments: Do emails with attachments arrive completely?
Encoding: Are special characters and non-ASCII text rendered correctly?
From/Reply-To: Are the sender and reply addresses correct?

Rendering testing

Mobile rendering: Does the email look correct on mobile devices?
Desktop clients: Does it render correctly in Outlook, Gmail, Apple Mail, and Thunderbird?
Dark mode: Does the email adapt correctly to dark mode settings?
Image blocking: Does the email remain readable when remote images are blocked?
Plain text fallback: Is the plain text version present and complete?
Alt text: Do images have appropriate alt text for accessibility?

Functionality testing

Links work: Do all links in the email navigate to the correct destination?
Unsubscribe works: Does the unsubscribe link actually unsubscribe the user?
One-time links: Do magic links work on first use only?
Expiration: Do time-limited links expire at the correct time?
UTM parameters: Are tracking parameters preserved in links?

Security testing

SPF/DKIM/DMARC: Do authentication checks pass for the sending domain?
HTML sanitisation: Is HTML sanitised to prevent XSS in email clients?
Link safety: Are links checked against malicious URL databases?
Attachment safety: Are attachments scanned for malware before delivery?
Header exposure: Do email headers expose sensitive internal information?

Spam filter testing

Spam checkers: Use tools like GlockApps or Mail-Tester to check spam scores
Recipient testing: Test delivery to Gmail, Outlook, and corporate mail systems
Complaint monitoring: Monitor for spam complaints in your email provider dashboard
Reputation monitoring: Check if your domain or IP appears on any blocklists

Using temporary email for QA

Temporary email is particularly useful for QA teams because:

It provides a clean external recipient without existing filters or rules
You can generate a fresh address for each test without polluting your real inbox
It shows email rendering with images blocked, revealing fallback issues
It confirms delivery is happening at all, independent of recipient-side filtering
It allows testing with different recipient types without needing real test accounts

For automated CI pipelines, use a local mail catcher (MailHog, Mailpit) or a dedicated testing service with an API. Temporary email is best for manual spot-checks and exploratory testing.

Questions

How often should I run email testing?

Run full email testing before each release and after any significant changes to email templates, sending infrastructure, or authentication configuration. Run smoke tests daily to catch regressions. For high-volume senders, monitor delivery metrics continuously.

What is the most common email testing mistake?

Assuming that successful API response means successful delivery. A 200 OK from your email provider only means the message was handed off, not that it was delivered to the recipient. Always verify actual receipt in test inboxes.