Email is one of the most critical channels in modern software. From password resets and account verification to payment confirmations and multi-factor authentication (MFA), email workflows are often the final step between a working feature and a real user experience.
Yet despite its importance, email testing is frequently overlooked in QA strategies, especially in automated pipelines. When email failures slip through, they’re usually discovered by users first.
This guide explains how to test emails reliably in CI/CD, covering manual and automated approaches, common pitfalls, and how QA and engineering teams can build confidence in every email they send.
Why email testing matters
Even teams with strong application test coverage regularly encounter email-related failures, including:
- Missing test emails in staging
- Environment-specific deliverability failures
- False positives in CI pipelines
- Broken links, expired OTPs (one-time passcodes), or missing verification codes
Without automated checks for outgoing emails, these issues often go unnoticed until production, damaging trust and delaying activation or conversion.
Email testing ensures that your emails are sent when expected, content is correct and personalised, links, tokens, and OTPs work as intended, and finally that messages render correctly across clients and devices.
The complexity of email testing in CI/CD
Automated email testing brings huge benefits but introduces unique challenges in CI/CD environments.
Emails rely on infrastructure outside your application, such as SMTP servers, inboxes, and third party providers, where small delays or configuration mismatches can cause flaky tests.
An example of an issue in CI/CD pipelines is when emails arrive too late for the next step of the flow, leading to failed tests. Alternatively, the verification tokens within the emails may expire before validation, or your emails may behave inconsistently across environments.
To scale confidently, email testing in CI/CD must be designed with reliability in mind.
The 4 essential types of email tests
A robust strategy covers multiple layers:
| Test type | What is it | An example |
|---|---|---|
| Functional email tests | Check the key functionality of your emails; whether they were triggered by the correct action, sent properly etc. | Sign up to your product as though you are a user. Check your account verification email landed as you intended. |
| Content validation checks | Check the content of the emails, including personalisation and links and codes. | At the beginning of your email, you expect it to say “Hello, [first name]”. Test this with different account names and see if the first name changes accordingly. |
| Layout and rendering tests | Whether the layout and rendering of the emails looks as expected across different email clients and devices. | You use an email testing tool to generate screenshots of your emails across Apple and Android products, as well as email clients – now you can see if your emails render as you anticipated and if you need to make any changes. |
| Deliverability and anti spam tests | These tests ensure your emails land where you anticipate and aren’t sent to spam. This often requires realistic staging environments and controlled inboxes. | You send your email to a realistic staging environment, and it arrives to spam. Now you know what will happen when sending it to real users, so can make the necessary changes. |
Key challenges in email testing
QA and DevOps teams often face these pain points:
Dependency on external email services
Using production services like SendGrid or SES in test environments can trigger rate limits or even send incomplete test emails to real users. This means that tests can fail because servers temporarily reject or throttle messages.
Environment configuration issues
Staging environments often lack production parity. SMTP ports may be blocked, authentication misconfigured, or inboxes shared across tests. This can mean that your testing environment doesn’t truly reflect the real-life flow of your emails, so can leave your unprepared for issues when you hit send.
Parsing dynamic content
Emails frequently include OTPs, 2FA codes, password reset links, and personalised data. Extracting and validating this content automatically can be difficult without a specific email testing tool to do so.
Security and data isolation
Test data must never cross into real user inboxes. Dedicated, isolated test inboxes are essential for compliance and control.
Buy-in across teams
Email testing sits between engineering, QA, DevOps, and sometimes marketing, making ownership unclear without the right processes.
Approaches to automating email tests
Fake SMTP servers and local stubs
Commonly set up for development and testing purposes, these are especially useful for testing your email functionality and are usually more reliable than mocking email-sending libraries and classes.
Email testing APIs and sandbox environments
Tools like Mailosaur capture emails sent during tests and expose them via an API for email testing. This allows QA teams to not only assert that emails were sent, but also to validate content, links, and OTPs, test end to end workflows, and avoid real inboxes entirely. This approach is also ideal for automated email testing in CI/CD pipelines.
How to test emails in popular frameworks
Email testing can be integrated directly into countless frameworks, including Selenium, Cypress and Playwright, which can all be used to test end-to-end workflows.
Using an email testing API such as Mailosaur means tests can wait for messages to arrive, extract verification codes, and complete flows automatically. In fact, Mailosaur offers quick start guides for your framework, so that you’ll be all set up in just a few lines of code.
Best practices for email testing in CI/CD
1. Use dynamic inboxes By using dynamic inboxes in your testing, you’ll avoid clashes in parallel pipelines because you’ll remove the risk of flaky testing caused by the wrong email being picked up in your automated flows.
2. Test both delivery and content Some teams choose to test that their email arrives, but not what’s within it, or vice versa. This is an incredibly risky business either way, because you could end up with perfect emails that don’t arrive, or defective emails that do; both of which erodes customer trust.
3. Validate OTP timing, expiry, and correctness It’s not enough to ensure that your one-time passcodes merely arrive and work. Your customers will be expecting them to arrive instantly, work flawlessly, and expire within a suitable amount of time. Without testing all of these elements, you’re not just risking trust, but there are also compliance risks when OTPs used for authentication don’t expire as they should.
4. Clean up or expire test data automatically By doing this, you’ll ensure test reliability, system performance, and security, as well as preventing the accumulation of ‘stale’ data which can lead to false test results, increased costs, and hidden security vulnerabilities.
5. Avoid Gmail or shared inbox “workarounds” Using shared inboxes such as a Gmail account means your tests will lack the accuracy, security, and scalability required for professional quality assurance. Relying on them often leads to inaccurate testing results, security breaches, and inefficient workflows, and limit your control of your testing.
Although these may seem like a lot of changes to your current testing practices, thankfully they can all be achieved easily with an email testing tool.
Email testing tools, such as Mailosaur, allow you to create unlimited inboxes for your testing, preventing clashes in your pipelines. Beyond this, they provide you with a simple and intuitive interface to test delivery and content, allow you to have maximum control of your testing (setting your own parameters for how long your data is kept for, who can access each inbox, and generate screenshots to test rendering across devices), and make automating end-to-end tests simple.
The good news
Email failures are some of the most visible and damaging bugs a product can ship, but also some of the easiest to rectify. Whether you’re validating password resets, OTP emails, or transactional notifications, email testing is a critical part of modern QA and building and maintaining the trust of your customers.
By adopting automated email testing, integrating with tools like Selenium, Cypress, or Playwright, and using a dedicated email testing API, teams can catch issues before users ever see them.