List-ID

What is a List-ID in Emailing?

The List-ID is an email header that uniquely identifies a mailing list. It allows receiving mail servers and email clients to recognize that a message belongs to a specific list, helping with message organization, filtering, and delivery decisions. Each mailing list should have a consistent List-ID value so recipients and automated systems can distinguish one list’s messages from another’s.

The header was standardized in RFC 2919 and is included in the header section of each message distributed by a mailing list manager. When properly configured, it ensures that list traffic is easily identifiable and can be handled separately from normal person-to-person mail.

How the List-ID Header Works

A List-ID header appears in this format:

The portion inside the angle brackets represents a unique domain-like identifier. It does not need to resolve in DNS, but it must be globally unique. When mail clients see this header, they can group or filter related messages automatically, making it easier for users to manage list subscriptions.

Other common mailing list headers that work alongside List-ID include:

• List-Unsubscribe – provides a direct link or mailto address for unsubscribing
• List-Help – specifies contact information or documentation for the list
• List-Owner – identifies the administrator of the list
• List-Post – shows how to post messages to the list

These headers improve email deliverability, compliance with anti-spam regulations, and the user experience of managing subscriptions.

List-ID in Authentication and Filtering

Although the List-ID header does not play a direct role in DMARC or SPF validation, it can influence how receiving systems treat messages from mailing lists. When combined with valid authentication results, List-ID helps mail providers recognize legitimate list messages and reduce false spam classifications.

Some lists modify message headers or resend mail on behalf of the original sender, which can break DKIM signatures. In these cases, receiving systems may use the List-ID and other headers to identify that the message came from a legitimate mailing list rather than a spoofing attempt. Advanced receivers take this into account when applying DMARC policy decisions.

List-ID and DMARCeye

DMARCeye helps organizations understand how their outbound and third-party mail streams behave across various authentication checks. By analyzing headers like List-ID, DMARCeye can differentiate between messages sent directly by your systems and those distributed through mailing lists that modify message content.

This visibility helps identify legitimate mail that fails authentication due to list forwarding or rewriting. DMARCeye highlights these edge cases so you can adjust your policies or work with trusted providers to maintain deliverability and compliance across all email channels.

Sign up for a free trial of DMARCeye today and secure your email domain.

To learn more about DMARC and DMARC-related terms, explore the DMARCeye Glossary.