The header.i tag in an email header, specifically within the DKIM (DomainKeys Identified Mail) signature, serves as an identifier for the agent or user responsible for signing the email. While header.from represents the visible sender address (the RFC 5322 From header), header.i (or i= in the DKIM-Signature) points to the signing identity, often a subdomain or specific email address under the primary d= (domain) tag. This distinction is crucial for email authentication protocols like DKIM, which help verify sender authenticity and prevent spoofing.
While header.i is an optional field primarily used for internal tracking by the sending system, its alignment with the header.from domain can impact overall sender reputation and deliverability. Misconfiguration or inconsistencies in these headers can flag emails as suspicious, potentially leading to lower inbox placement rates or even blacklisting. Proper DKIM setup and alignment are essential for maintaining a strong sender reputation.
Email marketers often encounter complexities within email headers when troubleshooting deliverability issues. The relationship between header.i, header.from, and the overall DKIM signature can be a source of confusion, particularly when trying to understand how different domains interact and affect sender reputation.
Many marketers focus on ensuring their emails are authenticated correctly without diving too deep into the minutiae of each header tag, often relying on their ESPs (Email Service Providers) to manage these technical aspects. However, a basic understanding of these elements is crucial for diagnosing authentication failures and improving inbox placement.
Marketer view
Email marketer from Email Geeks indicates they are trying to understand the discrepancy between header.i being the sending domain and header.from being the organizational domain. This suggests a common challenge in interpreting complex email headers for authentication purposes.
Marketer view
Email marketer from Email on Acid highlights that a DKIM signature helps mailbox providers verify the sender and prevent phishing attacks like email spoofing. This underscores DKIM's foundational role in email security and deliverability.
Email deliverability experts typically view header.i as an important, albeit secondary, component of the DKIM authentication process. While the d= tag (signing domain) is paramount, header.i (identity) provides granular detail about the specific entity within that domain that initiated the email. Experts emphasize that the core purpose of header.i is for internal accountability, rather than a primary external reputation factor, although its consistency and proper alignment can still play a role.
The consensus among experts is that any element in an email that is measured by receiving servers can influence reputation, but only if it's consistently associated with negative user interactions (e.g., spam complaints, low engagement). Therefore, focusing on overall good sending practices and authentication remains key.
Expert view
Expert from Email Geeks indicates that the 'i=' tag within a DKIM signature identifies a more specific identity responsible for the signature. This identity can be either an email address or a subdomain of the 'd=' domain, providing granular detail on the signing entity.
Expert view
Expert from Word to the Wise explains the difference between DKIM's 'i=' and 'd=' tags, noting that 'i=' allows a more specific identity to take responsibility for the signature. This distinction is crucial for understanding how DKIM signatures attribute responsibility for email authentication.
Official documentation and standards, such as those from the IETF (Internet Engineering Task Force) that define DKIM, clarify the role of the header.i tag. The i= tag, or 'identity', specifies the entity within the signing domain responsible for the message. While it's optional, its presence helps in granular attribution of responsibility for the DKIM signature.
Documentation also highlights that email authentication protocols like SPF, DKIM, and DMARC are designed to verify sender identity and prevent various forms of email abuse, including spoofing. The interplay of different header domains is crucial for these protocols to function correctly and build sender reputation, even if direct matching isn't always mandated.
Technical article
Documentation from Mailgun states that email authentication protocols like SPF, DKIM, and DMARC are crucial for verifying sender identity, preventing spoofing, and supporting a strong sender reputation. These protocols work in concert to establish trust in the email ecosystem.
Technical article
Documentation from Mailjet highlights that email headers help verify message security during transit and confirm it reached the recipient without errors or alterations. This underscores the header's role as a diagnostic tool for delivery and integrity issues.
10 resources
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