Where can I find a list of all mailbox providers and their domains?
Michael Ko
Co-founder & CEO, Suped
Published 4 Jun 2025
Updated 19 Aug 2025
9 min read
When you're dealing with email deliverability, knowing who the mailbox provider is for any given domain can be incredibly helpful. You might be looking to understand specific sending policies, troubleshoot issues, or simply segment your audience more effectively. It seems straightforward enough, but you'll quickly discover that a truly complete and up-to-date list of all mailbox providers (MBPs) and their domains is notoriously hard to find.
The reason for this difficulty lies in the dynamic nature of the email ecosystem. While a handful of major players dominate the landscape, there are thousands of smaller internet service providers (ISPs), educational institutions, businesses, and even individuals who host their own email services using custom domain names. These entities can also use third-party email services, which further complicates identification.
The continuous mergers, acquisitions, and technological shifts mean that any static list becomes outdated almost as soon as it's published. Instead of searching for a definitive, exhaustive list that likely doesn't exist, it's more practical to understand the major players and learn effective methods for dynamically identifying mailbox providers as needed. Let's explore why this is the case and how you can approach this challenge.
Major players in the email ecosystem
While an exhaustive list is elusive, it's undeniable that a few key mailbox providers handle the vast majority of consumer email traffic. Understanding these dominant forces is crucial, as their policies and infrastructure significantly impact your email deliverability. The 'MAGY' group – Google (Gmail), Apple (iCloud Mail), Microsoft (Outlook.com, Hotmail, Live), and Yahoo (Yahoo Mail, AOL Mail) – collectively manage a significant portion of global email traffic.
Each of these major players uses a primary domain, such as gmail.com, outlook.com, or yahoo.com, but they also operate numerous other domains, including country-specific domains like hotmail.co.uk or live.ca, as well as domains acquired through past mergers or consolidations. For example, some ATT.net domains are routed through Yahoo's infrastructure. You can often find lists of the most popular email domains, like this one at email-verify.my-addr.com, which can give you a general idea of market share.
These major providers are constantly evolving their infrastructure and policies. What holds true today might change tomorrow, particularly with respect to their filtering mechanisms and how they interact with specific sending domains. This makes staying updated on their practices vital for good deliverability. For more information on identifying these, refer to our guide on main domain names used by large free email providers.
Mailbox Provider
Primary Domains
Example Other Domains
Google (Gmail)
gmail.com
googlemail.com, hotmail.com (for some corporate accounts)
Beyond these large providers, many regional ISPs and smaller email services exist. While they might handle less overall volume, they are still important targets for your email campaigns. Their domain names can vary widely, from generic names to highly specific regional ones, making them difficult to track without dynamic lookup methods. This is why a static list is often insufficient for comprehensive coverage. For deeper insights into how domain reputation is measured by these providers, read our guide on understanding your email domain reputation.
The evolving landscape of email domains
The core challenge in compiling a complete list of mailbox providers and their domains is the sheer scale and fluidity of the internet. Every organization, from a small business to a large university, can choose to host its own email servers or use a third-party service under its unique domain name. This means there are literally millions of active email domains, far too many to compile into a single, manageable, and perpetually accurate list.
Furthermore, the ownership and routing of these domains are constantly changing. Companies merge, acquire smaller entities, or divest parts of their business. When this happens, email domains can be redirected, absorbed into larger networks, or even discontinued. For instance, an ISP might consolidate its email services under a parent company, or a smaller provider could be acquired by a major one, leading to changes in how their mail is routed and processed.
For example, in the past, Cox's email services were transitioned to Yahoo, meaning emails sent to cox.net addresses are now handled by Yahoo's infrastructure. These kinds of shifts are ongoing and can impact how you categorize or target different domains. It's not just about listing domains, but also understanding who is ultimately responsible for receiving and filtering mail for those domains.
The challenge is further compounded by legacy domains and absorbed networks that still exist but might be filtered by a larger parent company. This means the entity that appears to own the domain on the surface might not be the ultimate mail handler, adding another layer of complexity to identification efforts.
The dynamic nature of email domains
A static list of all mailbox providers and their domains will almost always be incomplete or outdated. The email landscape is constantly shifting, with new domains emerging and existing ones changing hands or being rerouted. Relying on such a list exclusively can lead to inaccurate targeting and potential deliverability issues.
Dynamic identification of mailbox providers
Given the dynamic nature of email domains, the most reliable way to identify a mailbox provider for a specific email address or domain is through real-time lookup methods. The primary method involves querying the domain's Mail Exchanger (MX) records. MX records are a type of DNS record that specifies which mail servers are responsible for accepting email messages on behalf of a recipient's domain and where those emails should be routed.
By performing an MX record lookup for a domain (e.g., example.com), you can see the hostname of the mail server that handles emails for that domain. This hostname often contains clues about the actual mailbox provider, even if it's a third-party service. For example, an MX record pointing to mx.google.com clearly indicates Google is the provider.
While you can do this manually using command-line tools, for a large number of domains, automated solutions are necessary. Some email validation services or deliverability platforms offer tools that can perform these lookups at scale, providing you with the associated mailbox provider for each domain in your list. These tools are far more efficient than trying to maintain a manual list. To learn more about this, explore our article on how to determine the ISP or mailbox provider.
Example MX record lookup using dig (Linux/macOS)BASH
dig MX example.com
Manual MX lookup
Performing manual MX record lookups provides direct, real-time data about the mail servers for a domain. This can be done using command-line tools like dig or nslookup. It's good for individual checks or small-scale investigations.
Benefits: Provides the most current information. No reliance on third-party data or APIs. Direct insight into mail routing.
Drawbacks: Time-consuming and impractical for large lists. Risk of being flagged as abusive by some mail servers if too frequent, as mentioned in the slack discussion.
Automated identification tools
Various online tools and APIs specialize in identifying mailbox providers by analyzing MX records at scale. These services abstract away the technical complexity and provide categorized results.
Benefits: Efficient for bulk processing. Often provides additional data points like domain reputation or disposable email detection. Tools for identifying providers.
Drawbacks: Can incur costs for large volumes. Data accuracy may vary between providers. Reliance on external services.
Beyond the giants: ISPs and temporary domains
Beyond the big four, the email landscape is fragmented, comprising thousands of smaller ISPs, corporate mail servers, educational institutions, and more. These providers might not handle the same volume as Google or Microsoft, but they are still important targets for many senders. Their domains are often tied to specific regions or organizations, making them less predictable than generic webmail addresses.
A particular subset of domains that warrant attention are disposable email domains (DEDs), also known as temporary or throwaway email addresses. These domains are used to generate short-lived email addresses often for signing up for services without revealing a permanent email address. While these are not traditional mailbox providers, identifying them is crucial for maintaining a clean and effective email list.
Sending to DEDs can inflate your bounce rates, lead to higher spam complaint rates (as these addresses are often used for abuse), and even contribute to your IP or domain being added to a blacklist or blocklist. Many email security and deliverability platforms maintain and update lists of these domains for suppression purposes. You can find more information about these in our article on where to find a list of temporary email service domains. Understanding and avoiding these types of domains is a key aspect of successful email sending.
The risks of disposable email addresses
Sending emails to disposable email addresses (DEDs) can severely harm your sender reputation and deliverability. These addresses often have high bounce rates and can quickly turn into spam traps (or be associated with blocklists), negatively impacting your inbox placement. It's essential to filter them out of your mailing lists to maintain a healthy sender reputation.
Navigating the email domain landscape
While the idea of a comprehensive, static list of all mailbox providers and their domains is appealing, the reality of the email landscape makes it an unachievable goal. The sheer volume of domains, coupled with constant changes through mergers, acquisitions, and evolving hosting solutions, means such a list would be obsolete almost immediately.
Instead, the most effective approach for email senders is to focus on understanding the major mailbox providers and, crucially, to implement dynamic methods for identifying the responsible mail handlers for individual domains. Utilizing MX record lookups, whether manually or through automated tools, provides the most current and accurate data for navigating this complex environment and ensuring your emails reach their intended inboxes. Regularly monitoring your deliverability and adapting to changes remains key to success in email marketing.
Views from the trenches
Best practices
Actively monitor your bounce rates and email deliverability across various domains to quickly identify issues.
Use MX record lookups to identify the actual mailbox provider for each email address on your list.
Segment your audience based on mailbox providers (e.g., Google, Microsoft, Yahoo) to tailor sending strategies.
Keep an eye on industry news for mergers and acquisitions that might impact domain routing.
Common pitfalls
Relying solely on outdated or incomplete static lists of mailbox providers and their domains.
Neglecting to remove or suppress disposable email addresses from your mailing lists, leading to reputation damage.
Ignoring high bounce rates from certain domains, which can indicate unmonitored changes in mail routing.
Assuming all domains ending in '.com' are handled by the same generic provider without verification.
Expert tips
Focus on domain reputation. Mailbox providers assess your sending domain's reputation to filter emails. A strong reputation with the major players matters more than knowing every single domain.
Dynamic lookup tools are your friends. Invest in or utilize tools that can perform real-time MX record lookups to determine the actual mail handler for any domain.
Pay attention to SMTP banners if you're doing advanced diagnostics. They often reveal the underlying mail server software and can sometimes hint at the actual provider, though direct MX lookups are generally safer and sufficient.
For large-scale sending, categorize your email lists by major mailbox providers and then monitor engagement within each category. This helps you identify specific issues with certain providers.
Expert view
Expert from Email Geeks says no single list of mailbox providers can ever be truly complete due to the sheer volume of custom domains and various hosting services.
2024-01-22 - Email Geeks
Expert view
Expert from Email Geeks says the best approach is to build your own evolving data set based on observed sends and dynamic lookups, as the landscape constantly changes.
Google (Gmail), 
Apple (iCloud Mail), 
Microsoft (Outlook.com, Hotmail, Live), and 
Yahoo (Yahoo Mail, AOL Mail) – collectively manage a significant portion of global email traffic.
Apple (iCloud Mail)
