What is the utility of X-Originating IP in email headers?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 May 2025
Updated 19 Aug 2025
8 min read
When delving into email headers, you often encounter fields that aren't immediately obvious in their purpose. The X-Originating-IP header is one such example. It’s a non-standard header, meaning it’s not formally defined in the main email RFCs, but it has been widely adopted by many mail transfer agents (MTAs) and webmail services over the years. Its primary function is to identify the IP address of the client that initially sent the email, especially when that client connects through a web interface or a proxy.
While its utility has evolved and in some cases diminished with increased privacy considerations from major email providers like Microsoft and Google, understanding its historical role and current implications can still be valuable. It provides a unique piece of forensic data that can sometimes reveal the true origin of an email, aiding in security investigations and spam detection. Let’s explore what it is and why it matters.
Historical and current context
The X-Originating-IP header is a custom header that records the IP address of the user or system that initiated the email transmission. Unlike the standard Received headers, which log every server the email passes through, X-Originating-IP specifically aims to pinpoint the client's IP. This is particularly useful when someone sends an email via a webmail interface or a mail service that acts as a proxy, obscuring the direct connection.
Historically, this header was a key tool in combating spam and abuse. Before the advent of more sophisticated outbound filtering mechanisms, email providers (especially webmail services) would include this header to help downstream receivers identify and block spammers. If a webmail account was compromised and used to send large volumes of spam, the X-Originating-IP provided a direct link to the source of the malicious activity. This allowed receiving mail servers to implement selective blocking based on the originating IP, even if the sending service itself wasn't entirely blocklisted (or blacklisted).
Today, while still present in some emails, its prevalence has decreased. Many major email providers have opted to remove or obfuscate this header for privacy reasons, or they manage abuse through other means, such as encrypted cookies or internal tracking systems. For more on custom headers, consider reading about how X-headers impact deliverability.
However, for smaller mail services or those not handling massive volumes, the X-Originating-IP can still provide valuable insights. It’s particularly relevant for scenarios where email is sent directly from a user's client application or a simple script connecting to an SMTP server, rather than through a complex webmail system. This header, when present, serves as a direct, unmediated link to the sender's origin.
Utility in email forensics
The X-Originating-IP header shines brightest in email forensics and abuse detection. When investigating suspicious emails, such as phishing attempts, malware distribution, or spam campaigns, identifying the originating IP address is a crucial first step. While the Received headers provide a trail of servers, the X-Originating-IP pinpoints the system where the message was composed or initially submitted.
Security analysts can take this IP address and perform a WHOIS lookup to determine the Internet Service Provider (ISP) or organization that owns that IP range. This information can then be used to report abuse to the relevant ISP, which might lead to the suspension of the malicious actor's account. This type of detailed tracing is essential for uncovering the source of unwanted email. For more information on how to identify the ESP of a spam email, see how to identify the ESP from headers.
Another critical use case is checking if the originating IP is listed on any email blocklists (or blacklists). While IP addresses from major mail providers are typically well-managed, an X-Originating-IP that belongs to a smaller, less reputable source might appear on such lists. If an email is sent from an IP that's blocklisted, it significantly increases the chances of it being rejected or sent to the spam folder. Knowing this can help diagnose deliverability issues.
Here's an example of where you might find this header in an email:
Example email headerstext
Received: from mail.example.com (mail.example.com [192.0.2.1])
by recipient.net (Postfix) with ESMTP id ABCDE12345
for <user@recipient.net>; Thu, 4 Nov 2021 10:00:00 +0000 (GMT)
X-Originating-IP: [203.0.113.45]
Message-ID: <unique-id@example.com>
Date: Thu, 4 Nov 2021 10:00:00 +0000
From: Sender Name <sender@example.com>
To: Recipient Name <user@recipient.net>
Subject: Test Email
In this example, 203.0.113.45 would be the IP address of the client that initially connected to mail.example.com to send the email.
Deliverability impact
While useful for forensic analysis, does the X-Originating-IP directly impact your email deliverability as a sender? For most legitimate senders, the answer is generally no. Major mailbox providers primarily rely on other authentication protocols and reputation signals to determine inbox placement. These include SPF, DKIM, and DMARC, alongside sender reputation metrics associated with your sending IPs and domains.
However, there's an indirect impact. If your originating IP (the one recorded in this header) consistently sends spam or engages in abusive behavior, and this header is consistently present, it could lead to that specific IP being blocklisted. If the IP you use to send emails to an email service provider is blocklisted, this could prevent your emails from reaching their destination. It’s important to understand what happens when your IP is blocklisted (or blacklisted).
The primary concern for most senders regarding IP addresses should be the reputation of their outbound sending IP, rather than the originating IP itself, unless they are directly responsible for managing the initial client connection point. For a detailed discussion on this, you might find value in exploring the question, Does X-Originating-IP impact email deliverability?
For email service providers and large organizations, deciding whether to include or remove the X-Originating-IP header involves a trade-off between privacy and forensic utility. Removing it can enhance user privacy, but it might slightly hinder abuse investigations for external parties. This balance is carefully weighed, particularly by services that handle a high volume of user-generated emails. You can also explore whether this header should be removed.
Conclusion
The X-Originating-IP header, while no longer universally present or as critical for mainstream deliverability as it once was, still serves a specific purpose in the email ecosystem. Its utility lies primarily in its ability to trace the initial point of email submission, particularly from webmail interfaces or clients that connect directly to an SMTP server. This makes it a valuable data point for security teams, abuse desks, and forensic investigators when trying to understand the provenance of suspicious or unwanted emails.
For email senders focused on deliverability, attention should remain on established authentication standards and maintaining a strong sender reputation. However, understanding the role of X-Originating-IP provides a more complete picture of how email flows and how its origins can be uncovered. As email security continues to evolve, the historical context of headers like this offers insights into the ongoing efforts to combat abuse and ensure trustworthy communication.
Views from the trenches
Best practices
Always review email headers for suspicious emails to identify potential originating IPs.
Use reputable blocklist (blacklist) checking tools to verify if an IP is compromised or listed.
Report abusive originating IPs to their respective ISPs to help improve overall email hygiene.
Focus on robust email authentication (SPF, DKIM, DMARC) for primary deliverability efforts.
Common pitfalls
Assuming the X-Originating-IP is always present or the sole source of truth for email origin.
Not understanding that major providers increasingly obfuscate or remove this header.
Confusing the X-Originating-IP with the Received header's server IPs, which show transit points.
Over-relying on this header for general deliverability assessment rather than reputation metrics.
Expert tips
If an X-Originating-IP points to a webmail system, it usually indicates the user's browser IP.
For smaller email setups like those using PHP-Mailer, this header might accurately reflect the sending system's IP.
The header was initially instrumental for receivers to block spammers sending through compromised webmail accounts.
Its utility for abuse reporting remains, allowing providers to pinpoint the source of malicious activity.
Expert view
Expert from Email Geeks says the X-Originating-IP typically identifies the browser that connected to the webmail system.
2019-11-04 - Email Geeks
Expert view
Expert from Email Geeks says the X-Originating-IP started before effective outbound filtering, allowing receivers to block spammers sending through webmail providers.
Microsoft and 
Google, understanding its historical role and current implications can still be valuable. It provides a unique piece of forensic data that can sometimes reveal the true origin of an email, aiding in security investigations and spam detection. Let’s explore what it is and why it matters.
