Message-ID

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title: "Message-ID" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["unique-identifiers", "email", "usenet"] description: "Unique identifier for a digital message" topic_path: "general/unique-identifiers" source: "https://en.wikipedia.org/wiki/Message-ID" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Unique identifier for a digital message ::

Message-ID is a unique identifier for a digital message, most commonly a globally unique identifier used in email and Usenet newsgroups.

Message-IDs are required to have a specific format which is a subset of an email address and be globally unique. No two different messages must ever have the same Message-ID. If two messages have the same Message-ID, they are assumed to be the same and one version is discarded. This can cause issues if tools mangle the IDs created by other tools. Such a problem has been reported with Google MTAs mangling Message-IDs created by Outlook, making it difficult to reference other messages and breaking threading.

Message-IDs, if present, are generated by the client program sending the email or by the first mail server. A common method of generating such ID is by combining the time and domain name, for example: 950124.162336@example.com.

References

References

1. Eoghan Casey. (2004). "Digital evidence and computer crime: forensic science, computers and the Internet". [[Academic Press]].
2. Resnick, P.. (October 4, 2008). "Internet Message Format".
3. Klensin, J.. (October 4, 2008). "Simple Mail Transfer Protocol".
4. Levinson, E.. (August 4, 1998). "Content-ID and Message-ID Uniform Resource Locators".

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::