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

Key findings

• 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.
• 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.
• 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.
• 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

• Internal education: Educate development and QA teams on proper email testing protocols, emphasizing the risks of using real external email addresses.
• Controlled environments: Implement and enforce the use of controlled testing environments that do not route email to external internet mailboxes.
• Reputation monitoring: Actively monitor sender reputation metrics and be prepared to take corrective action if issues arise, such as contacting ISPs.
• 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

• Developer errors: Marketers frequently express frustration over developers inadvertently using real email addresses for automated testing, leading to severe deliverability problems.
• 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.
• 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.
• Internal solutions: Marketers advise using internal staff mailboxes, dummy accounts, or specialized test environments to prevent external deliverability impacts.

Key considerations

• Strict guidelines: Implement clear, non-negotiable guidelines for email testing within development and QA workflows to avoid critical mistakes.
• Automated testing: For automated tests, ensure that no mail leaves your control. Utilize tools designed for email testing in isolated environments.
• 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.
• 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

• Test domain usage: Experts strongly recommend using reserved domains like .invalid or .test for any testing that involves non-existent email addresses.
• Isolated environments: Using tools like MailHog or Mailtrap for email capturing in development environments is essential to prevent unintended outbound email.
• 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.
• 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

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

Key findings

• RFC standards: RFCs explicitly designate certain domains, such as .test and .invalid, as non-routable for testing, preventing accidental outbound email.
• Authentication: Proper email authentication protocols (SPF, DKIM, DMARC) are fundamental for establishing sender legitimacy and are detailed in various RFCs and ISP guidelines.
• 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.
• 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

• Adhere to RFC 2606: Always use reserved domains for testing to ensure that test emails do not inadvertently reach the live internet.
• Implement authentication: Ensure your sending infrastructure correctly implements SPF, DKIM, and DMARC to comply with email authentication best practices.
• 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.
• Content optimization: Follow documented guidelines for email content and design to avoid triggering spam filters and ensure optimal inbox placement.