Summary
Uncovering the email sending domain and Email Service Provider (ESP) details primarily involves a thorough analysis of email headers. Key information can be found by viewing the 'original' or 'full headers' of an email in clients like Gmail or Outlook. Within these headers, specific fields such as 'Received' headers reveal the email's path and IP addresses, while the 'Return-Path' often indicates the domain used for bounce management. Authentication records like SPF, DKIM, and DMARC, visible in the 'Authentication-Results' header, are crucial for identifying the legitimate sending domain and can point to authorized ESPs. Additionally, performing IP address lookups on the IPs found in the 'Received' headers can frequently identify the ESP. While some ESPs white-label sending domains, their unique server names or 'X-' headers can still provide clues. For efficiency, online email header analyzer tools can parse these complex details, making it easier to pinpoint the sender's infrastructure.
Key findings
- Email Header Analysis: Analyzing email headers is the primary and most reliable method to find email sending domain and ESP details. Key headers to examine include 'Received', 'Return-Path', 'Authentication-Results', 'X-Mailer', and 'Message-ID'.
- Client-Specific Access: In email clients like Gmail and Outlook, users can access the full email headers by selecting options like 'Show original' or 'View message source'. These full headers contain all the necessary technical details.
- Tracing IP Addresses: The 'Received' headers contain the sender's IP address and server names. Using an IP lookup tool, such as WHOIS, can reveal the organization owning that IP block, which is frequently the Email Service Provider or a related data center.
- Authentication Records (SPF, DKIM, DMARC): The 'Authentication-Results' header provides details from SPF, DKIM, and DMARC checks. The 'd=' tag in the DKIM signature typically reveals the actual signing domain. Furthermore, analyzing a domain's public DNS records, specifically SPF and DKIM entries, can explicitly name or implicitly point to ESPs authorized to send emails on behalf of that domain.
- Return-Path Header: The 'Return-Path' header often indicates the domain used by the ESP for bounce management. For emails sent through an ESP, this typically points to a subdomain of the ESP (e.g., mcdlv.net for Mailchimp).
- Online Header Analyzers: Various online email header analyzer tools exist that can parse complex email headers, simplifying the identification of the originating IP, various 'Received' domains, and sometimes directly identifying the Email Service Provider from specific header fields.
Key considerations
- ESPs and White-Labeling: Email Service Providers (ESPs) often allow users to white-label their sending domains, meaning the 'Return-Path' and DKIM signatures might point to the user's custom domain rather than the ESP's. Despite this, the underlying ESP can often still be identified by the IP addresses in the 'Received' headers, which are typically associated with the ESP's infrastructure.
- Bottom-Up Header Analysis: When manually analyzing 'Received' headers, it is advised to trace these lines from the bottom up. This approach helps identify the initial sending server's IP and hostname, providing a clearer path to the origin.
- ESP-Specific Footprints: Some ESPs insert unique 'X-' headers, like 'X-Mailgun-Campaign-Id' or 'X-ConstantContact-Message-ID', or use distinctive server naming conventions in 'Received' lines. Recognizing these specific footprints can provide direct clues about the ESP.
- Not Always Definitive: While effective, identifying the true sending domain and ESP often requires careful, manual analysis of multiple header fields and external lookups, as no single field is always definitive.
What email marketers say
11 marketer opinions
To pinpoint an email's sending domain and its originating Email Service Provider (ESP), a deep dive into the email's full headers is essential. This detailed inspection involves examining several critical header fields. The 'Received' headers provide a chronological trail of servers and their corresponding IP addresses, crucial for tracing the email's path. The 'Return-Path' header often reveals the domain designated for handling bounces, which can frequently be an ESP's subdomain. For robust authentication insights, the 'Authentication-Results' header details SPF, DKIM, and DMARC checks, with the DKIM 'd=' tag being particularly useful for identifying the true signing domain. Further insights into the ESP can be gained by performing IP lookups on addresses found in the 'Received' headers, often revealing the owning organization. While ESPs may white-label domains or mask their presence, specific 'X-' headers and distinctive server naming conventions can sometimes betray their identity. Utilizing online email header analyzer tools streamlines this complex analysis, making the identification process more efficient for marketers.
Key opinions
- Comprehensive Header Examination: The 'Received' headers offer a chronological path of servers and IPs; 'Return-Path' identifies the bounce management domain; 'Authentication-Results' provides SPF, DKIM, and DMARC insights crucial for sender legitimacy and ESP clues via the DKIM 'd=' tag.
- IP Address Tracing: Extracting IP addresses from 'Received' headers and performing WHOIS or IP lookup queries can directly identify the ESP or its associated infrastructure.
- ESP-Specific Signatures: Beyond standard headers, some ESPs embed unique 'X-' headers, like 'X-Mailer', 'X-Provider', or custom tracking IDs, or use recognizable naming conventions in their server hostnames within 'Received' lines, serving as direct fingerprints of the service.
- Leveraging Online Tools: Online email header analyzer tools, such as liveinboxer.com, effectively parse complex header data, simplifying the identification of sending domains, IPs, and often directly identifying the underlying ESP.
- Message-ID Clues: While not always definitive, the domain part of the 'Message-ID' header can occasionally point to the system that generated the message, offering a potential clue about the sending domain or ESP.
Key considerations
- White-Labeling Challenges: Email Service Providers frequently allow clients to white-label their sending domains, meaning the 'Return-Path' and DKIM signatures might point to the user's custom domain rather than the ESP's. In such cases, identifying the ESP relies more heavily on IP address lookups and unique ESP-specific headers.
- Manual Header Traversal: When manually reviewing 'Received' headers, it is most effective to trace them from the bottom up. This approach helps pinpoint the initial sending server's IP and hostname, providing a clearer path to the origin.
- Multi-Faceted Analysis: No single header field provides a complete picture; a combination of analyzing various headers, performing IP lookups, and recognizing ESP-specific footprints is often required to accurately determine the sending domain and ESP.
Marketer view
Marketer from Email Geeks explains that you can use liveinboxer.com to get ESP details, including the send server, or send the email to Gmail and click 'view original' to retrieve similar information.
25 Dec 2022 - Email Geeks
Marketer view
Marketer from Email Geeks responds by offering access to similar tools and asks what specific information is being sought from the eDataSource screenshot to help provide the relevant data.
26 Dec 2024 - Email Geeks
What the experts say
2 expert opinions
Determining an email's sending domain and its associated Email Service Provider (ESP) is primarily accomplished through a meticulous examination of the email's technical headers. Critical headers to scrutinize include 'Received,' which provides a chronological log of servers and their IP addresses, and 'Return-Path,' often indicating the domain used for handling bounces. Further insights come from the 'DKIM-Signature' and 'Authentication-Results' headers, as these reveal SPF, DKIM, and DMARC verification details that confirm the legitimate sending domain. Supplementing this header analysis, performing reverse DNS lookups on the IP addresses discovered within the 'Received' headers can further clarify the sender's identity and pinpoint the specific Email Service Provider responsible for the transmission.
Key opinions
- Header Analysis as Foundation: Experts emphasize that the examination of an email's full headers, particularly fields like 'Received', 'Return-Path', 'DKIM-Signature', and 'Authentication-Results', is fundamental to identifying sending domain and ESP details.
- Tracing Email Path with 'Received': The 'Received' headers are crucial for tracing the email's journey through servers and for extracting the associated IP addresses, which are key to uncovering the sender's infrastructure.
- Bounce Address Clues from 'Return-Path': The 'Return-Path' header often contains the bounce address, which can reveal the domain or server responsible for bounce management and frequently points to the sending ESP.
- Domain Identity via Authentication: Authentication headers, including 'DKIM-Signature' and 'Authentication-Results' (for SPF and DMARC), are vital as they directly link the email to its authenticated sending domain.
- IP Address Lookups for ESPs: Analyzing the IP addresses found in 'Received' headers and performing reverse DNS lookups on them can effectively identify the underlying Email Service Provider or the organization behind the sending server.
Key considerations
- Holistic Header Review: Accurately identifying the sending domain and ESP requires a comprehensive review of multiple header fields, as no single header provides all the necessary information in isolation.
- Leveraging Reverse DNS: Performing reverse DNS lookups on the IP addresses found in the 'Received' headers is a critical step, as it can directly reveal the hostname and often the organization or ESP associated with the sending server.
- Authentication for Domain Verification: The 'DKIM-Signature' and 'Authentication-Results' headers, which detail SPF, DKIM, and DMARC checks, are essential for verifying the legitimate sending domain and can offer strong clues about the authorized Email Service Provider.
Expert view
Expert from Spam Resource explains that identifying the email sending domain and ESP involves examining email headers like 'Received', 'Return-Path', 'DKIM-Signature', and SPF records. Analyzing IP addresses in 'Received' headers and performing reverse DNS lookups can further reveal the sender's identity and service.
17 Apr 2022 - Spam Resource
Expert view
Expert from Word to the Wise shares that email headers are key to finding sending domain and ESP details. Important headers include 'Received' (to trace email path and IPs), 'Return-Path' (for the bounce address, often linked to the sending server), and 'Authentication-Results' (for DKIM, SPF, and DMARC, which tie to the sending domain).
11 Jul 2022 - Word to the Wise
What the documentation says
5 technical articles
Uncovering an email's sending domain and its associated Email Service Provider (ESP) requires a multi-faceted approach, primarily involving the inspection of an email's full headers and a review of the sender's public DNS records. Within email clients like Outlook and Gmail, users can access the 'message source' or 'original' view to reveal comprehensive headers. These headers contain vital clues such as the chronological trail of servers and IP addresses in 'Received' headers, the bounce domain in 'Return-Path', and hints about the sending software or ESP in fields like 'X-Mailer'. Beyond header analysis, examining the sender's public DNS records, specifically SPF and DKIM, is paramount. These records often explicitly list or point to authorized ESPs, particularly through 'include:' directives in SPF. Even when custom domains are used to white-label sending, ESPs frequently leave identifiable traces within the 'Received' headers, making it possible to ascertain the underlying service.
Key findings
- Email Client Header Access: Users can find detailed email sending domain and ESP information by viewing the message source or full headers in email clients like Outlook ('View message source' or 'full headers') and Gmail ('Show original' via the three-dots menu).
- Header Fields for Identification: Key information within email headers includes the sender's IP address and server names found in 'Received' headers, the sending domain typically indicated by 'Return-Path', and clues about the sending software or ESP in fields like 'X-Mailer' or 'Authentication-Results'.
- Public DNS Records (SPF, DKIM): Examining the sender's public DNS records, specifically SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) entries, is crucial for identifying ESPs authorized to send emails for that domain, as these records often explicitly name or imply the service.
- ESPs' Header Footprints: Email Service Providers, even when supporting custom domains, often leave identifiable footprints in email headers. For instance, Mailgun's server names and IP addresses typically appear in 'Received' headers, helping to confirm it as the underlying ESP.
Key considerations
- Combined Analysis Required: Accurately identifying the email sending domain and ESP often necessitates a dual approach, combining the detailed analysis of email headers with an examination of the sender's public DNS records like SPF and DKIM.
- SPF 'include' Directives: SPF records are particularly useful as they frequently contain 'include:' directives that explicitly list third-party mail services or ESPs authorized to send on behalf of the domain, such as 'include:spf.protection.outlook.com' for Microsoft 365.
- White-Labeling and Header Clues: Even when a custom sending domain is used, potentially white-labeling the 'Return-Path' or DKIM, the underlying ESP can often still be identified through their specific server names and IP addresses visible in the 'Received' headers.
Technical article
Documentation from Microsoft Support explains that users can find email sending domain and ESP details by viewing the message source or full headers in Outlook. Key information like the sender's IP address, server names in "Received" headers, and fields such as "X-Mailer" or "Return-Path" can reveal the sending infrastructure and potentially the ESP.
13 Feb 2025 - Microsoft Support
Technical article
Documentation from Google Support explains that to identify the email sending domain and ESP, users should open the email in Gmail, click the three dots next to the reply button, and select "Show original." This reveals the full email headers, where "Received" headers indicate the sending server, "Return-Path" often shows the sending domain, and other headers like "Authentication-Results" or "X-Mailer" can give clues about the ESP.
4 Apr 2022 - Google Support
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