Which email domains are grouped under major providers?
Michael Ko
Co-founder & CEO, Suped
Published 12 May 2025
Updated 26 Aug 2025
7 min read
The sheer volume of email domains can be overwhelming. For anyone engaged in email marketing or bulk sending, understanding which domains are grouped under major providers is not just helpful, it's critical. These groupings, often encompassing multiple well-known domains, share underlying infrastructure and, importantly, share sender reputation.
Navigating this landscape effectively means recognizing that a message sent to hotmail.com might be handled by the same systems that process mail for outlook.com or live.com. This consolidation has significant implications for your deliverability, determining whether your emails land in the inbox or are redirected to spam (or even rejected outright).
Understanding major email provider groupings
Major Mailbox Providers (MBPs) consolidate multiple email domains under a single entity to streamline operations, enhance security, and manage user experiences. This means that a unified set of rules and algorithms governs email reception across these grouped domains. For example, a single provider might manage domains that appear distinct to the casual user, such as gmail.com and googlemail.com, or yahoo.com and aol.com. Understanding these connections is essential for email deliverability, as actions impacting one domain often affect others within the same group.
For senders, this grouping translates directly into how their email campaigns perform. A poor sending reputation with one domain in a group can negatively impact delivery to all domains managed by that same provider. It underscores the need for a holistic approach to email hygiene and compliance, rather rigorous analysis of each domain. You can learn more about how to identify the underlying provider by checking out this guide on what tools and methods can be used to identify the mailbox provider associated with an email address or domain.
While precise, exhaustive, and constantly updated lists are difficult to maintain due to the dynamic nature of mergers and acquisitions, several key groupings are widely recognized in the email industry. Here’s a summary of the most prominent ones and their associated domains.
Provider
Primary Domains
Associated Domains
Google
gmail.com
googlemail.com, youtube.com (less common for email)
tutanota.com, fastmail.com (generally not grouped)
The dynamic nature of domain ownership
The email landscape is not static, and major providers frequently acquire or merge with other services, leading to shifts in domain groupings. For instance, Verizon Media Group (now part of Apollo Global Management as Yahoo, Inc.) once managed a vast array of domains including Yahoo, AOL, and others, significantly impacting a large segment of email users. Understanding these shifts is crucial because an email address that once belonged to one system might now be governed by another, complete with new filtering rules and deliverability policies.
Relying on outdated information or simple regular expressions can lead to miscategorization of recipients and potential deliverability issues. What was once accurate for a specific domain might no longer hold true after an acquisition or a change in infrastructure. For up-to-date information, resources like the MAGY Domains List: 2025 Update from Spam Resource are invaluable, offering insights into these evolving relationships.
While direct ownership changes can be complex to track, you can often identify the underlying email service provider for a specific domain by checking its Mail Exchange (MX) records. These DNS records indicate which mail servers are responsible for accepting email for a domain. By performing an MX lookup, you can see if multiple domains point to the same set of mail servers, suggesting they might be managed by the same provider. This can be a key method for how you can determine the ISP or mailbox provider of an email address.
However, MX records only tell part of the story, as some providers may use different MX records for different domains even if they share the same backend filtering logic. Thus, a comprehensive approach often combines MX record analysis with awareness of industry news and updated lists.
Example MX record lookup for yahoo.comBASH
dig MX yahoo.com +short
Impact on email deliverability and sender reputation
Grouping domains under major providers means they often share not only infrastructure but also sender reputation systems. This has profound implications for email deliverability. If your sending practices lead to high spam complaints or poor engagement metrics for one domain, the negative reputation (or blocklist listing) can extend across all domains within that provider's group. This unified reputation management by large providers can quickly escalate a minor issue into a widespread deliverability problem, affecting your ability to reach a significant portion of your audience. For example, a minor issue can quickly lead to what happens when your domain is on an email blacklist.
Mailbox providers like Google and Microsoft employ sophisticated filtering algorithms that consider numerous factors, including IP reputation, domain reputation, content, and user engagement. When these systems detect suspicious activity or consistently low engagement from a sender to any domain within their group, they can impose stricter filtering, rate limits, or even outright rejections. This is why a consistent, high-quality sending strategy across all your lists, regardless of the individual email domain, is paramount.
To maintain good sender reputation and optimize inbox placement, it's vital to segment your email lists based on mailbox providers where possible. This allows for tailored sending strategies that adhere to each provider's specific best practices and connection limits. For example, understanding what Microsoft domains you should exclude from your email segmentation can prevent unnecessary filtering.
Maintaining a positive sender reputation
Regularly monitor your sender reputation and adjust sending volumes and frequency based on performance.
List hygiene: Periodically clean your email lists to remove inactive or invalid addresses, reducing bounce rates and spam trap hits.
Authentication: Ensure all your emails are properly authenticated with a simple guide to DMARC, SPF, and DKIM to build trust with mailbox providers.
Engagement: Focus on sending relevant content that encourages positive engagement, such as opens and clicks, across all grouped domains.
Strategies for effective email management
Given the evolving landscape of email domain groupings, adopting a proactive and adaptive strategy for your email programs is crucial. Static lists of domains quickly become outdated, and relying on them can lead to overlooked deliverability challenges. Continuous monitoring of your email performance across different providers helps you quickly identify and address potential issues, such as increased bounce rates or spam folder placement.
Furthermore, major providers like Google and Yahoo are continuously updating their sender requirements, emphasizing strong authentication and low spam rates. This includes authentication standards like DMARC, SPF, and DKIM. These standards help providers verify your sending legitimacy across all their grouped domains, thereby reducing the likelihood of your emails being flagged as suspicious. Learn more about the main domain names used by large free email providers and ISPs.
Effective email management in this environment requires moving beyond generic sending practices. Instead, it involves a nuanced approach that accounts for the consolidated nature of major email providers.
Traditional approach: static domain lists
Outdated data: Relies on lists that quickly become inaccurate due to mergers and acquisitions.
Missed connections: Fails to recognize new domain groupings under major providers.
Generic strategy: Applies a one-size-fits-all sending approach, missing provider-specific nuances.
Reputation blind spots: Doesn't account for shared reputation across grouped domains, leading to unexpected deliverability issues.
Modern approach: dynamic monitoring
Real-time updates: Incorporates dynamic data sources and tools to track domain ownership changes.
Accurate segmentation: Enables precise segmentation based on current provider groupings.
Tailored sending: Allows for customized sending practices that align with each major provider's requirements.
Proactive reputation management: Monitors performance across all grouped domains, addressing issues before they escalate.
Views from the trenches
Best practices
Regularly consult updated lists of grouped domains from reliable industry sources to ensure your segmentation is accurate.
Verify MX records for domains you send to, as they can reveal the underlying mailbox provider.
Implement and monitor email authentication protocols like SPF, DKIM, and DMARC consistently across all your sending domains.
Segment your email lists by major mailbox provider to tailor sending strategies and manage reputation effectively.
Common pitfalls
Relying on outdated regex patterns for domain grouping, leading to incorrect categorization and deliverability problems.
Assuming all domains are independent, thereby failing to recognize shared infrastructure and reputation impacts.
Neglecting to check MX records, missing critical clues about which provider is handling mail for specific domains.
Failing to adapt sending practices when a major provider acquires new domains or shifts its infrastructure.
Expert tips
Always verify new domain lists against multiple sources or tools, as consolidation and disaggregation are ongoing processes.
Consider the implications of shared infrastructure on IP and domain reputation when planning your email campaigns.
Keep an eye on industry announcements regarding mergers or changes in provider policies to stay ahead of deliverability challenges.
Understand that even if a domain isn't explicitly listed, its MX records can sometimes reveal its alignment with a major provider.
Marketer view
Marketer from Email Geeks says: "I found that the more comprehensive lists, like those compiled by experienced deliverability experts, are much more reliable than trying to create regex patterns from scratch."
August 17, 2025 - Email Geeks
Expert view
Expert from Email Geeks says: "Our organization manages hundreds of consumer domains and tens of thousands of small business domains, and our ownership has changed since 2021, so old groupings might not apply."
August 17, 2025 - Email Geeks
Navigating the clustered email universe
Understanding which email domains are grouped under major providers is no longer a niche concern but a fundamental aspect of successful email deliverability. By staying informed about these groupings, leveraging tools to identify underlying providers, and adapting your sending strategies accordingly, you can significantly improve your inbox placement and protect your sender reputation. The email ecosystem is constantly evolving, and proactive management is key to ensuring your messages reach their intended recipients.
Google
Microsoft
Yahoo/Verizon Media Group
Apple
GMX/1&1
protonmail.com
tutanota.com, 
fastmail.com (generally not grouped)
