What are the best practices for email testing to avoid deliverability issues?

Key findings

1. Avoid live mailboxes: Sending automated tests to actual, public email addresses (like test@hotmail.com) is highly detrimental to sender reputation and can trigger spam traps.
2. Reserved domains: Domains like .invalid and .test are specifically reserved by IETF for testing purposes and will never route on the public internet, making them safe for internal development.
3. Test environments: Isolated test environments (e.g., local SMTP servers or dedicated email testing platforms) are critical for simulating email sends without affecting live deliverability.
4. Reputation damage: Repeatedly sending to non-existent or spam trap addresses can lead to IP and domain blocklistings, severely impacting legitimate email campaigns.

Key considerations

1. Internal education: Educate development and QA teams on proper email testing protocols, emphasizing the risks of using real external email addresses.
2. Controlled environments: Implement and enforce the use of controlled testing environments that do not route email to external internet mailboxes.
3. Reputation monitoring: Actively monitor sender reputation metrics and be prepared to take corrective action if issues arise, such as contacting ISPs.
4. Policy enforcement: Establish clear policies regarding what constitutes an acceptable test email address and ensure compliance across all teams involved in email sending.

Key opinions

1. Developer errors: Marketers frequently express frustration over developers inadvertently using real email addresses for automated testing, leading to severe deliverability problems.
2. Spam trap risks: There is a strong consensus that sending to unowned or common test addresses can activate spam traps, which are designed to identify problematic senders.
3. Accidental spamming: Real-world anecdotes illustrate how easily test environments, if improperly configured, can accidentally send unsolicited emails to legitimate customer lists, damaging sender reputation.
4. Internal solutions: Marketers advise using internal staff mailboxes, dummy accounts, or specialized test environments to prevent external deliverability impacts.

Key considerations

1. Strict guidelines: Implement clear, non-negotiable guidelines for email testing within development and QA workflows to avoid critical mistakes.
2. Automated testing: For automated tests, ensure that no mail leaves your control. Utilize tools designed for email testing in isolated environments.
3. Regular review: Regularly review your email sending practices to ensure compliance with best practices and to catch any issues early before they escalate to deliverability problems.
4. Deliverability impact: Understand that even seemingly minor testing missteps can result in your emails being flagged as spam or blocklisted, as highlighted by email deliverability best practices.

Key opinions

1. Test domain usage: Experts strongly recommend using reserved domains like .invalid or .test for any testing that involves non-existent email addresses.
2. Isolated environments: Using tools like MailHog or Mailtrap for email capturing in development environments is essential to prevent unintended outbound email.
3. No live smarthosts: Connecting test environments to live smart hosts is considered dangerous and can lead to significant deliverability issues, including being added to a blocklist.
4. Spam trap activation: Repeated sending to inactive or commonly used test accounts can trigger spam traps, which negatively impacts email deliverability for all subsequent mail.

Key considerations

1. Policy enforcement: Establish clear internal policies for email testing that forbid sending to unowned or live external mailboxes.
2. Simulated sending: Utilize simulated sending environments that capture emails for inspection rather than sending them to actual inboxes, providing full control and visibility.
3. Header inspection: When testing in owned mailboxes, verify email headers to ensure authentication (SPF, DKIM, DMARC) is correctly configured and passing.
4. Preventing spam: Proactive measures, such as proper testing protocols, are essential for avoiding spam folders and maintaining a positive sending reputation.

Key findings

1. RFC standards: RFCs explicitly designate certain domains, such as .test and .invalid, as non-routable for testing, preventing accidental outbound email.
2. Authentication: Proper email authentication protocols (SPF, DKIM, DMARC) are fundamental for establishing sender legitimacy and are detailed in various RFCs and ISP guidelines.
3. ISP tools: Major email providers (e.g., Google, Microsoft) offer postmaster tools and data services to help senders monitor their reputation and diagnose deliverability issues.
4. Content guidelines: Documentation often provides guidelines on email content, warning against practices like image-heavy emails or excessive links that can trigger spam filters.

Key considerations

1. Adhere to RFC 2606: Always use reserved domains for testing to ensure that test emails do not inadvertently reach the live internet.
2. Implement authentication: Ensure your sending infrastructure correctly implements SPF, DKIM, and DMARC to comply with email authentication best practices.
3. Utilize feedback loops: Register for and actively monitor feedback loops and postmaster tools from major ISPs to gain insights into how your emails are perceived and delivered.
4. Content optimization: Follow documented guidelines for email content and design to avoid triggering spam filters and ensure optimal inbox placement.