How can I determine the ISP or mailbox provider of an email address?

9 Marketer opinions 3 Expert opinions 3 Technical articles 5 Resources

Summary

Determining the ISP or mailbox provider of an email address involves a multi-faceted approach, with MX record analysis being a central technique. Examining the domain name after the '@' symbol offers a basic clue, but querying MX records provides more reliable information about the mail servers responsible for the domain. For a deeper dive, analyze A records, PTR records, and WHOIS data related to those mail servers. Distinguish between Google (gmail-smtp-in.l.google.com, etc.) and Microsoft (olc.protection.outlook.com, etc.) domains. Reverse DNS lookups can help identify the organization operating the mail server. Tools like MXToolbox and PowerShell's Get-DnsClient facilitate MX record retrieval. Email validation APIs and email append services offer alternative routes, albeit potentially at a cost. Be mindful that the identified mail server isn't always the ISP, and consider data privacy implications when using paid services. Utilizing dedicated IPs provides direct access to ISP/Mailbox Provider information. Analyzing for patterns and grouping by commonalities from the different methods is also useful.

Key findings

MX Records are Key: MX record analysis is the primary method to identify the mail server and, by extension, the likely email provider.
Multiple DNS Lookups: Combining MX record lookups with A record, PTR record, and WHOIS data analysis can provide a more complete picture.
Email Validation/Append Services: Email validation APIs and email append services can supplement DNS lookups, but may come with a cost and privacy considerations.
Mail Server vs. ISP: The identified mail server may not be the recipient's ISP; it indicates the email service provider.
Dedicated IPs Provide Info: Dedicated IPs provide direct access to recipient ISP and Mailbox provider information.

Key considerations

Complexity of Analysis: Analyzing DNS records and interpreting the results can be technically complex.
Cost of Services: Email validation and append services can incur costs.
Data Privacy: Be mindful of data privacy regulations (e.g., GDPR) when using email validation and append services.
Accuracy Limitations: No single method is foolproof; combining methods improves accuracy.
Dynamic Nature: Email infrastructure and DNS records can change, so the information is not always static.

What email marketers say
9Marketer opinions

Determining the ISP or mailbox provider of an email address involves several methods, each with varying degrees of reliability. Examining the domain after the '@' symbol and performing MX record lookups are common approaches. MX records reveal the mail servers responsible for handling email for a domain, which can often identify the provider (e.g., Google Workspace, Microsoft 365). More advanced techniques involve analyzing A records, PTR records, and even WHOIS data. Email validation APIs and email append services can also provide this information, though often at a cost. It's important to note that identifying the *ISP* specifically can be challenging, as the mail server is not always hosted by the ISP.

Key opinions

MX Records: MX record lookups are the most common and reliable method for identifying the mail server used by a domain.
Email Validation APIs: Email validation APIs can provide additional details beyond basic DNS lookups, such as deliverability status and provider information.
Email Append Services: Email append services offer additional data enrichment, including ISP/mailbox provider information.
Not Always the ISP: The mail server identified is not always the ISP of the email address's owner.
Multiple Techniques: A combination of techniques, including MX record analysis, A/PTR record analysis, and WHOIS lookups, can improve accuracy.

Key considerations

Reliability: Some methods, like relying solely on the domain after the '@' symbol, are less reliable than others.
Cost: Email validation APIs and email append services often come at a cost.
Data Privacy: Consider data privacy regulations and ethical implications when using email validation and append services.
Accuracy: No single method guarantees 100% accuracy. Combining methods improves the likelihood of identifying the correct provider.
Dedicated IP: If you are using a dedicated IP for your email you will have access to recipient's ISP/Mailbox provider data.

Marketer view

Email marketer from Mailjet shares that they provide information about the recipients ISP/Mailbox Provider when using a dedicated IP. This is because it is beneficial to split emails by provider, e.g., Gmail, Hotmail, Yahoo etc to gain optimal deliverability.

April 2024 - Mailjet

Marketer view

Email marketer from Medium responds to the question. You can utilize email marketing tools or services that offer subscriber information, including location and ISP details. These tools often use IP address geolocation and other data to enrich subscriber profiles.

March 2023 - Medium

Marketer view

Email marketer from Email Hippo explains that email append services which often provide extra data such as demographics, also append an email address's ISP or mailbox provider.

January 2023 - Email Hippo

Marketer view

Email marketer from Email Geeks shares a method to identify the ISP/mailbox provider of an email address by looking up the domain's MX records, then the MX's A records, then the A's PTRs, and optionally whois the IPs, grouping by commonalities.

July 2024 - Email Geeks

Marketer view

Email marketer from Quora responds to the question. You can identify the host of an email address by looking at the part after the @ symbol. The host is typically also the ISP. Do an IP lookup for the host to determine the email address's location and network provider.

January 2025 - Quora

Marketer view

Email marketer from Reddit suggests using email validation APIs (like AbstractAPI, Kickbox, or ZeroBounce) to get information about an email address, including deliverability status, whether it's a disposable email, and sometimes the provider. These tools perform various checks, including DNS lookups and SMTP verification.

February 2022 - Reddit

Marketer view

Email marketer from Email Geeks shares to check `*.<http://protection.outlook.com|protection.outlook.com>` and `*.<http://google.com|google.com>` for MX Lookups to identify Microsoft365 vs. Google Workspace addresses.

June 2022 - Email Geeks

Marketer view

Email marketer from LinkedIn suggests using an email validation service to get the ISP and mailbox provider of a user. This will return additional details associated with an email address.

March 2022 - LinkedIn

Marketer view

Email marketer from Stack Overflow explains you can't reliably determine the *ISP* of an email address. You can only determine the *mail server* the domain uses by looking up the MX record. The ISP hosts the domain but is not necessarily the mail provider.

November 2023 - Stack Overflow

What the experts say
3Expert opinions

Determining the ISP or mailbox provider of an email address involves a combination of DNS lookups and domain analysis. One approach is to examine the domain name after the '@' symbol, but more complex scenarios require querying MX records to identify the responsible mail servers. Analyzing these MX records, particularly by classifying them (e.g., Google vs. Microsoft domains), provides insight into the email provider. Reverse DNS lookups can also help identify the organization responsible for an IP address, potentially revealing the operating mail server or infrastructure.

Key opinions

MX Record Analysis: Querying and classifying MX records is a key method to identify the email provider (e.g., distinguishing Google and Microsoft domains).
Reverse DNS Lookups: Reverse DNS lookups can reveal the organization operating the mail server, which may be an ISP or corporate entity.
Domain Name Examination: Examining the domain name after the '@' can provide a basic indication, but is insufficient for complex cases.

Key considerations

Complexity: Advanced scenarios may require more sophisticated techniques beyond simply looking at the domain name.
Custom Domains: MX records are crucial for identifying providers when custom domains are in use.
SQL for Classification: SQL functions and scripts can be used to automate and classify MX records for easier identification.

Expert view

Expert from Word to the Wise shares that reverse DNS lookups can help identify the organization responsible for an IP address. While this doesn't directly give you the "ISP", it can reveal the company or entity operating the mail server, which can often be a large ISP or a corporate mail infrastructure.

February 2024 - Word to the Wise

Expert view

Expert from Spam Resource explains that determining the email provider often involves looking at the domain name after the '@' symbol. For more complex scenarios, performing a DNS lookup, specifically querying the MX records, can reveal the mail servers responsible for handling email for that domain. These MX records will often indicate the actual provider, even if the domain is custom.

April 2023 - Spam Resource

Expert view

Expert from Email Geeks shares she has a SQL function that does DNS lookups on the MXs, and a SQL script that classifies the raw MXs, splitting out Google domains (gmail-smtp-in.l.google.com, gmr-smtp-in.l.google.com, googlemail.com, aspmx.l.google.com, psmtp.com) and Microsoft domains (olc.protection.outlook.com, mail.protection.outlook.com, mail.outlook.com).

November 2022 - Email Geeks

What the documentation says
3Technical articles

Determining the ISP or mailbox provider of an email address relies heavily on examining MX records. These records, as explained in Google Workspace Admin Help, pinpoint the mail servers responsible for a domain. Microsoft Learn highlights the use of PowerShell's Get-DnsClient cmdlet for programmatic MX record queries. MXToolbox provides an MX Lookup tool for instant MX record checks, simplifying the process of identifying the mail servers.

Key findings

MX Records are Key: MX records are the definitive source for identifying mail servers handling email for a domain.
Programmatic Access: PowerShell's Get-DnsClient enables programmatic access to MX records.
MX Lookup Tools: Tools like MXToolbox provide a quick and easy way to check MX records.

Key considerations

Programmatic vs. Manual: Choose between programmatic methods (PowerShell) and manual tools (MXToolbox) based on the scale and automation needs.
Underlying Domain: Remember that MX records point to the *mail server*, not necessarily the ISP of the email address owner; it identifies the *mail provider*.
Multiple MX Records: A domain can have multiple MX records, indicating backup or load-balanced mail servers.

Technical article

Documentation from MXToolbox explains that their MX Lookup tool allows you to instantly check a domain's MX records. This provides information about the mail servers responsible for handling email for that domain.

October 2024 - MXToolbox

Technical article

Documentation from Microsoft Learn shares that you can use the Get-DnsClient cmdlet in Powershell to query DNS records, including MX records. This allows you to programmatically determine the mail servers for a given domain.

January 2024 - Microsoft Learn

Technical article

Documentation from Google Workspace Admin Help explains that MX records specify the mail servers responsible for accepting email messages on behalf of a domain name. You can look up the MX records to see where a domain's email is routed. Example: google.com will show the google mail servers

January 2025 - Google Workspace Admin Help

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