Summary
The overwhelming consensus from experts, marketers, and documentation sources is that a comprehensive, static list of all mailbox providers and their domains is unattainable due to the ever-changing email landscape, acquisitions, domain consolidations, and the sheer volume of domains. The most effective strategies involve building and dynamically adapting your own lists, focusing on major ISPs, understanding their specific policies and authentication requirements, monitoring engagement and bounce messages, and segmenting your audience based on their domains. Attempting to scrape MX records is discouraged unless performed ethically and responsibly. Relying on external services or pre-built lists is likely to result in outdated or incomplete information. Direct, authoritative lists don't exist, but IANA provides a list of TLDs, and insight can be gained from the postmaster tools of major providers.
Key findings
- Impossible Static List: A complete, static list of all email domains is impossible to maintain due to its dynamic nature.
- Build Your Own List: The most effective approach is to build your own list based on your specific audience and sending data.
- Focus on Major ISPs: Prioritize understanding the policies and authentication requirements of major ISPs (Gmail, Yahoo, Outlook, etc.).
- Dynamic Landscape: The email domain landscape is constantly changing due to acquisitions, consolidations, and new providers.
- Engagement is Key: Monitoring engagement metrics (opens, clicks) helps identify active domains and segment your audience effectively.
- IANA Provides TLDs: IANA provides a list of all valid top-level domains (TLDs), which serves as a starting point.
Key considerations
- Continuous Adaptation: Be prepared to continuously adapt your list and strategies to reflect the evolving email landscape.
- Monitor Bounce Messages: Monitor bounce messages to identify new or problematic domains and adjust your sending practices accordingly.
- Segment Your Audience: Segment your audience based on their email domain to tailor your messaging and improve deliverability.
- Use Provider Tools: Utilize the postmaster tools and guidelines provided by major mailbox providers to optimize your sending practices.
- Ethical Scraping: If considering scraping MX records, proceed ethically and respect rate limits to avoid being flagged as abusive.
What email marketers say
11 marketer opinions
The consensus is that a comprehensive, static list of all mailbox providers and their domains is practically impossible to maintain due to constant changes, the vast number of domains, and the dynamic nature of email infrastructure. Instead, the advice centers around focusing on major providers, monitoring engagement and bounces, segmenting your own data, and building custom lists based on your specific audience. Relying on external services is not an advisable strategy.
Key opinions
- Impracticality: Maintaining a complete list is impractical due to constant changes and sheer volume.
- Dynamic Nature: Mailbox providers and their domains are constantly evolving (e.g., acquisitions, filtering layers).
- Segmentation: Segmenting your own audience by domain and tracking engagement is a more effective approach.
- Custom Lists: Building custom lists based on your own data or leads is recommended over relying on pre-built lists.
- MX Records Incomplete: MX records are an incomplete source of information.
Key considerations
- Focus on Major Providers: Prioritize monitoring major mailbox providers like Gmail, Yahoo, and Outlook.
- Monitor Engagement: Actively monitor email engagement (opens, clicks) to identify active domains.
- Track Bounce Messages: Analyze bounce messages to identify unrecognized or problematic domains.
- Ethical Scraping: If scraping MX records, do so ethically and respect rate limits.
- Custom List Maintenance: Custom lists require constant maintenance to stay up-to-date.
Marketer view
Email marketer from StackExchange explains that compiling a full list of email domains is an impossible task, and suggests focusing on largest domains and using DNS queries to determine email acceptance on a case-by-case basis. Mentions that many domains use external services so MX records are not a good way of figuring out the details.
3 Jan 2025 - StackExchange
Marketer view
Email marketer from Reddit shares that maintaining a list is difficult, and suggests scraping MX records using tools or scripts but to do it ethically and with respect to rate limits. Also warns that you might need to keep the lists yourself
30 May 2022 - Reddit
What the experts say
6 expert opinions
Experts agree that obtaining a comprehensive and static list of all mailbox providers and their domains is highly impractical, if not impossible. The landscape is constantly evolving due to acquisitions, domain consolidations, and the sheer volume of domains. The recommended approach involves building and adapting your own lists, focusing on major ISPs, understanding their policies, monitoring bounce messages, and segmenting based on your sending data. Collecting data using SMTP banners is discouraged due to potential abuse complaints. A focus on active monitoring and dynamic adaptation is key.
Key opinions
- Impossible Static List: A complete, static list of all email domains is impossible to maintain.
- Dynamic Landscape: The email domain landscape is constantly changing due to acquisitions and consolidations.
- Build Your Own List: The best approach is to build your own list and evolve it with each send.
- Focus on Major ISPs: Concentrate on understanding the policies of major ISPs.
- SMTP Banner Issues: Collecting data via SMTP banners can lead to abuse complaints.
Key considerations
- Adapt to Changes: Be prepared to constantly adapt your list to reflect changes in the email domain landscape.
- Monitor Sending Data: Actively monitor your sending data to identify the domains your recipients are using.
- Segment Your Lists: Segment your lists based on domain and engagement metrics.
- Monitor Bounce Messages: Use bounce messages to identify new and emerging domains.
- Understand ISP Policies: Thoroughly understand the sending policies and authentication requirements of major ISPs.
Expert view
Expert from Word to the Wise (Laura Atkins) emphasizes that a complete, static list of email domains is impossible to maintain. Instead, she advises focusing on monitoring your own sending data to identify the domains your recipients are using and segmenting your lists accordingly. She highlights the importance of using feedback loops and other monitoring tools to identify and address deliverability issues with specific domains.
4 Mar 2025 - Word to the Wise
Expert view
Expert from Email Geeks explains that with Yahoo, Google, and Microsoft’s corporate offerings and also lots of legacy, absorbed, consolidated and acquired domains, the best such a system could hope for would be to tell you is who answers when you knock.
16 Jan 2023 - Email Geeks
What the documentation says
5 technical articles
While a direct list of all mailbox providers and their domains is unavailable through these documentation sources, they offer valuable tools and insights. IANA provides a list of all valid domain extensions (TLDs). Google and Microsoft offer guidelines and insights into their own email infrastructures. MXToolbox provides tools to look up MX records to identify mail servers. RFCs offer standards for email deliverability.
Key findings
- No Direct List: None of the listed documentation provides a direct, comprehensive list.
- IANA's TLDs: IANA provides a list of all valid top-level domains (TLDs).
- Provider Insights: Google and Microsoft provide insights into their own email systems.
- MX Record Lookup: MXToolbox allows looking up MX records for domain identification.
- RFC Standards: RFCs outline standards for email deliverability and management.
Key considerations
- Use IANA as Starting Point: Use IANA's list of TLDs as a starting point for identifying potential domains.
- Review Google/Microsoft Guidelines: Familiarize yourself with Google and Microsoft's sending guidelines and infrastructure.
- Utilize MXToolbox: Use MXToolbox to look up MX records for specific domains of interest.
- Understand RFC Standards: Review RFCs to understand the technical standards governing email delivery.
Technical article
Documentation from Google Postmaster Tools provides guidelines for bulk email senders and includes information about Google's email infrastructure. While it doesn't offer a full list, it provides insights into how Google handles email and the domains they use.
29 Dec 2021 - Google Postmaster Tools
Technical article
Documentation from MXToolbox explains how to use their tools to look up MX records for specific domains. While they don't provide a full list, their tools can be used to identify the mail servers (and thus, potentially, the email providers) for given domains.
22 Feb 2022 - MXToolbox
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