Understanding who is sending your emails and through which Email Service Provider (ESP) is fundamental for maintaining good email deliverability. Whether you're a marketer, a system administrator, or a curious individual, knowing these details can significantly impact your email strategy and security.
The sending domain is the digital identity from which your emails originate, directly influencing how mailbox providers perceive your messages. The ESP, on the other hand, is the platform or service facilitating the sending, often leaving digital fingerprints within the email itself.
Uncovering this information helps you troubleshoot deliverability issues, verify authentication protocols like SPF, DKIM, and DMARC, and even analyze competitors' email strategies. It's a critical step in taking control of your email program.
The importance of sender identification
Identifying the sending domain and ESP details is crucial for several reasons related to email health and performance. Knowing this information allows you to proactively manage your sender reputation and troubleshoot potential problems before they escalate.
For instance, if your emails are consistently landing in spam folders or being blocklisted (blacklisted), pinpointing the exact sending domain and ESP can help diagnose the root cause, whether it's poor authentication, a compromised account, or shared IP reputation issues. It's about understanding the journey your email takes and who is responsible at each step.
Beyond troubleshooting, this insight is vital for competitive analysis. By identifying a competitor's ESP, you can gain an understanding of their email infrastructure, scale, and potentially their deliverability practices. This strategic intelligence can inform your own platform choices and email strategy.
Why knowing matters
Understanding your email sending domain and ESP helps you maintain a strong sender reputation, which is key to inbox placement. If you're experiencing email deliverability issues, knowing these details is the first step in diagnosing and resolving the problem. It allows you to check for proper email authentication, investigate potential blocklist (blacklist) listings, and ensure your sending practices align with industry standards.
Decoding email headers to find details
One of the most direct ways to find email sending domain and ESP details is by examining the email headers. These headers contain a wealth of technical information about the email's journey from sender to recipient. While they might look complex at first, key pieces of information are usually easy to spot.
To access email headers, you typically need to open the email in your email client and look for an option like 'Show original', 'View source', or 'Message details'. Once open, you'll see lines of code. Look for specific headers such as Received, Return-Path, Authentication-Results, or X-Mailer and X-ESMTP-Source. The Received headers, listed in reverse chronological order, reveal the servers the email passed through. These often contain server names or domains indicative of the ESP. For a more detailed look, you can consult our guide on how to determine an email sending platform from headers.
The Return-Path header typically shows the domain responsible for handling bounces, which is often controlled by the ESP. Similarly, X-Mailer or X-ESMTP-Source headers can directly name the ESP or the mail server software used. These hidden pieces of information are invaluable for email forensics.
Example email headerstext
Received: from mail.example-esp.com (mail.example-esp.com [192.0.2.10])
by mx.recipient.com with ESMTPS id A1B2C3D4E5
for <recipient@example.com>; Mon, 1 Jan 2024 12:00:00 -0000 (UTC)
Return-Path: <bounce@example-esp.com>
Authentication-Results: mx.recipient.com; spf=pass (sender IP is 192.0.2.10) smtp.mailfrom=example-esp.com; dkim=pass header.d=sendingdomain.com
X-Mailer: MyESP Mailer v3.0
Leveraging DNS records for insights
Beyond email headers, publicly available DNS records offer another powerful avenue for identifying email sending domains and ESP details. DNS records like MX, SPF, DKIM, and DMARC are essential for email authentication and routing, and they often contain clues about the email infrastructure in use.
MX (Mail Exchanger) records, for example, specify the mail servers responsible for receiving email for a domain. While they show where incoming mail goes, sometimes large ESPs will list their own domains in these records, especially if they are also hosting the mailboxes. SPF (Sender Policy Framework) records list authorized sending IP addresses and domains, often including the ESP's sending infrastructure. You can learn more about these protocols in our simple guide to DMARC, SPF, and DKIM.
DKIM (DomainKeys Identified Mail) records, identified by a 'selector' in the DNS, contain public keys used to verify email authenticity. The domain associated with the DKIM signature often reveals the ESP or the specific sending infrastructure. DMARC (Domain-based Message Authentication, Reporting & Conformance) records, on the other hand, specify policies for handling emails that fail SPF or DKIM checks and often include reporting URIs that can point back to the DMARC reporting service, sometimes hinting at the ESP. Understanding these authentication methods is key for email deliverability, as detailed by Mailgun's email authentication guide. To learn more about identifying vendors for DMARC enforcement, you can check our article on the best methods for identifying email sending vendors.
DNS Record
What it reveals
Clues for ESP identification
MX record
Specifies mail servers for incoming email.
Can sometimes show ESP domain if they handle mailbox hosting, like google.com for Gmail.
SPF record
Lists authorized IP addresses or hostnames allowed to send email on behalf of a domain.
Often includes include: statements pointing to ESP's sending domains.
DKIM record
Contains the public key for verifying digital signatures.
The DKIM d= tag often lists the ESP's domain or a subdomain associated with it.
DMARC record
Policy for email authentication failures and reporting.
The rua= tag for aggregate reports might point to a DMARC reporting service, indirectly revealing the ESP or associated services.
Using specialized methods and observable patterns
While email headers and DNS records provide robust technical details, there are also more practical, behavior-based methods and specialized tools that can help identify email sending domains and ESPs. These methods are particularly useful when you need quick insights without diving deep into technical specifics.
Many ESPs embed their branding or specific tracking domains within email links. For instance, the unsubscribe link or 'view in browser' link often contains a subdomain or URL directly related to the ESP, such as trk.espname.com. Additionally, some ESPs add unique identifiers in email footers or HTML comments that can be easily recognized. Specialized tools also exist to perform this lookup automatically, like the ESP Finder by Sendview. You can explore various approaches in our article on identifying the mailbox provider for an email address or domain.
Another method involves observing common email practices. Many companies use a subdomain for their email sending, such as mail.yourdomain.com, to distinguish it from their primary website domain. This is a common best practice to protect the main domain's reputation in case of deliverability issues. We cover more on this topic in our article on best practices for choosing an email sending domain.
Manual inspection
Email headers: Requires access to the full email source, looking for Received, Return-Path, and X-Mailer fields.
DNS lookups: Manual querying of MX, SPF, DKIM, and DMARC records for domain clues.
Link inspection: Hovering over unsubscribe or tracking links to reveal ESP subdomains.
Automated tools
ESP Finders: Online tools that analyze email headers or domain records to automatically identify the ESP.
DMARC reports: Aggregated reports provide data on sending sources, including ESPs sending on your behalf. More information is available in our article on DMARC reports from Google and Yahoo.
Domain reputation tools: Some tools offer insights into the sending IP addresses and associated domains.
Conclusion
By understanding the different ways to identify email sending domain and ESP details, you can gain valuable insights into email deliverability. From scrutinizing email headers to performing DNS lookups and leveraging specialized tools, each method offers a unique perspective on your email infrastructure.
Whether you're troubleshooting an issue, conducting competitive analysis, or simply aiming for better email security, mastering these techniques will empower you to make informed decisions and optimize your email program for optimal performance and inbox placement.
Views from the trenches
Best practices
Always use a dedicated sending subdomain to isolate your email reputation from your main brand domain.
Regularly monitor your email blocklist (blacklist) status and domain reputation using specialized tools to catch issues early.
Implement strong email authentication (SPF, DKIM, DMARC) consistently across all sending domains and ESPs.
Common pitfalls
Failing to check if an ESP is using your domain for shared sending without your knowledge, impacting your reputation.
Ignoring email header analysis, missing critical clues about unauthorized or problematic sending sources.
Not configuring reverse DNS (PTR records) for your sending IPs, leading to deliverability issues.
Expert tips
Use email deliverability testing tools to get a comprehensive report on your email's authentication and routing path.
Periodically send test emails to various mailbox providers to observe how they handle your messages and what headers are added.
For complex setups, consult with an email deliverability consultant to ensure proper configuration and monitoring.
Marketer view
Marketer from Email Geeks says checking the 'view original' option in Gmail is a simple way to access email headers and discover ESP details, including the sending server.
2024-01-15 - Email Geeks
Expert view
Expert from Email Geeks says that third-party tools can provide comprehensive ESP details, especially for large sending domains, offering insights beyond standard header analysis.
google.com for Gmail.
